KAFKA-17545: Removing process fetch queue

[apoorvmittal10]

The PR removed the process fetch queue as we have moved to share fetch purgatory. As the fetches are passed to purgatory hence close of SharePartitionManager can't validate if all fetches are completed on shutdown hence removed the test case. We shall add a test case in ReplicaManager which should guarantee that all share fetches are completed on shutdown.

Committer Checklist (excluded from commit message)

• [ ] Verify design and implementation
• [ ] Verify test coverage and CI build status
• [ ] Verify documentation (including upgrade notes)

[apoorvmittal10]

Future tasks associated with refactor:

KAFKA-17829 - We need to add an integration test which verifies that on shutdown of the delayed share fetch purgatory, the share fetch requests which are present inside the purgatory return with an erroneous future.