[MINOR][BUILD] Fix javadoc8 break

[HyukjinKwon]

What changes were proposed in this pull request?

These error below seems caused by unidoc that does not understand double commented block.

[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:69: error: class, interface, or enum expected
[error] * MapGroupsWithStateFunction<String, Integer, Integer, String> mappingFunction =
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:69: error: class, interface, or enum expected
[error] * MapGroupsWithStateFunction<String, Integer, Integer, String> mappingFunction =
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:70: error: class, interface, or enum expected
[error] * new MapGroupsWithStateFunction<String, Integer, Integer, String>() {
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:70: error: class, interface, or enum expected
[error] * new MapGroupsWithStateFunction<String, Integer, Integer, String>() {
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:72: error: illegal character: '#'
[error] * @Override
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:72: error: class, interface, or enum expected
[error] * @Override
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:73: error: class, interface, or enum expected
[error] * public String call(String key, Iterator<Integer> value, KeyedState<Integer> state) {
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:73: error: class, interface, or enum expected
[error] * public String call(String key, Iterator<Integer> value, KeyedState<Integer> state) {
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:73: error: class, interface, or enum expected
[error] * public String call(String key, Iterator<Integer> value, KeyedState<Integer> state) {
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:73: error: class, interface, or enum expected
[error] * public String call(String key, Iterator<Integer> value, KeyedState<Integer> state) {
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:73: error: class, interface, or enum expected
[error] * public String call(String key, Iterator<Integer> value, KeyedState<Integer> state) {
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:76: error: class, interface, or enum expected
[error] * boolean shouldRemove = ...; // Decide whether to remove the state
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:77: error: class, interface, or enum expected
[error] * if (shouldRemove) {
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:79: error: class, interface, or enum expected
[error] * } else {
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:81: error: class, interface, or enum expected
[error] * state.update(newState); // Set the new state
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:82: error: class, interface, or enum expected
[error] * }
[error] ^
[error] .../forked/spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:85: error: class, interface, or enum expected
[error] * state.update(initialState);
[error] ^
[error] .../forked/spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:86: error: class, interface, or enum expected
[error] * }
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:90: error: class, interface, or enum expected
[error] * </code></pre>
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:92: error: class, interface, or enum expected
[error] * @tparam S User-defined type of the state to be stored for each key. Must be encodable into
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:93: error: class, interface, or enum expected
[error] * Spark SQL types (see {@link Encoder} for more details).
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:94: error: class, interface, or enum expected
[error] * @since 2.1.1
[error] ^

And another link seems unrecognisable.

.../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:16: error: reference not found
[error] * That is, in every batch of the {@link streaming.StreamingQuery StreamingQuery},
[error]

Note that this PR does not fix the two breaks as below:

[error] .../spark/sql/core/target/java/org/apache/spark/sql/DataFrameStatFunctions.java:43: error: unexpected content
[error] * @see {@link DataFrameStatsFunctions.approxQuantile(col:Str* approxQuantile} for
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/DataFrameStatFunctions.java:52: error: bad use of '>'
[error] * @param relativeError The relative target precision to achieve (>= 0).
[error] ^
[error] 

because these seem probably fixed soon in #16776 and I intended to avoid potential conflicts.

How was this patch tested?

Manually via jekyll build

[HyukjinKwon]

Note that such many errors seem hiding more errors in the error messages. This starts to hide the more errors so I proposed this PR.

[HyukjinKwon]

cc @srowen.

[SparkQA]

Test build #72875 has finished for PR 16926 at commit 1ec22f0.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[dongjoon-hyun]

nit. In the PR description, a typo: jeykill -> jekyll

[dongjoon-hyun]

I removed my previous comment about java linter errors here.
Never mind about that.

[HyukjinKwon]

Thank you @dongjoon-hyun, @srowen and @felixcheung for your approvals and reviews.

[srowen]

Merged to master