remove annotation @Experimental

[wanqulou]

What changes were proposed in this pull request?

http://spark.apache.org/docs/latest/streaming-kafka-integration.html
spark-streaming-kafka-0-8 is deprecated and spark-streaming-kafka-0-10 is stable

[AmplabJenkins]

Can one of the admins verify this patch?

[HyukjinKwon]

Why don't we just leave it or mark them as deprecated.

[markhamstra]

Where is the discussion on these utility methods no longer being Experimental? I'm not saying that they are not stable, but the Kafka 0.10 API in general being considered to be stable doesn't preclude some Kafka-related methods from still being other than stable, and promoting API to stable (i.e. cannot be changed without a major release) is a pretty big deal.

[srowen]

Yeah, I think Experimental is over-used in the APIs. They just never get un-marked and lots of pretty old stuff, that de facto is just not changeable now, is still labeled this way. This seems to be more "DeveloperAPI" than "Experimental". Still, I also don't know the right answer for this code. Ping the author?

I figured we'd remove just about all current Experimental tags when, say, Spark 3 rolls around.

[srowen]

I'd close this, evaluate which Experimental tags look clearly 'wrong' (i.e. something long established in a public API) and then open a JIRA targeted at 3.0 to consider removing them.