Cleaning up deprecated pubsub code.

[sduskis]

No description provided.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@2fc4e55). Click here to learn what that means.
The diff coverage is 50%.

@@ Coverage Diff @@## master #4949 +/- ##
=========================================
Coverage ? 50.36% Complexity ? 23674 =========================================
Files ? 2233 Lines ? 225860 Branches ? 24952 =========================================
Hits ? 113744 Misses ? 103519 Partials ? 8597

Impacted Files	Coverage Δ	Complexity Δ
...cloud/pubsub/v1/StreamingSubscriberConnection.java	64.75% <0%> (ø)	9 <0> (?)
.../com/google/cloud/pubsub/v1/MessageDispatcher.java	85.56% <100%> (ø)	22 <2> (?)
...ain/java/com/google/cloud/pubsub/v1/Publisher.java	81.05% <100%> (ø)	26 <0> (?)

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