Clean up flink-contrib: Remove flink-streaming-contrib and migrate its class to other modules

[Bowen Li <bo...@offerupnow.com>]

Hello Flink devs,

I'd like to propose removinh of flink-contrib/flink-streaming-contrib and
migrate its classes to flink-streaming-java/scala, for the following
reasons:

1. flink-streaming-contrib is so small that has only 4 classes (3 java and
1 scala), which isn't worth a dedicated jar for Flink to distribute and
maintain it, and for users to deal with confusion and overhead of
dependency management
2. the 4 classes are logically more tied to flink-streaming-java/scala, and
thus can be easily migrated
3. flink-contrib is already crowded and noisy. It lacks a proper project
hierarchy, confusing both devs and users

More discussion details in FLINK-8167
<https://issues.apache.org/jira/browse/FLINK-8167> and FLINK-8175
<https://issues.apache.org/jira/browse/FLINK-8175>

Are there any objections to this?


* This can be the 1st step of cleaning up flink-contrib. Stay tuned

Thanks,
Bowen