[FLINK-20589] Remove old scheduling strategies

[rmetzger]

What is the purpose of the change

After the implementation of the pipelined region scheduler (FLINK-16430), we no longer need the old LazyFromSourcesSchedulingStrategy and EagerSchedulingStrategy strategies and the components required by it. In order to simplify the maintenance, I suggest to remove these components.

Brief change log

• This PR addresses the first three subtasks of FLINK-20589

Verifying this change

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• Does this pull request introduce a new feature? (yes / no)
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Last check on commit b0dd813 (Mon Dec 14 20:27:39 UTC 2020)

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[tillrohrmann]

Thanks for creating this PR @rmetzger. LGTM. +1 for merging.

[rmetzger]

Thanks a lot for the review! I'll merge this PR now!