Summary:
In addition to removing the earlier partially implemented garbage collection
logic from the BlobDB codebase, the patch also removes the test cases (as well as
the related sync points, as appropriate) that were only relevant for the old
implementation, and reworks the remaining ones so they use the new GC logic.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6278
Test Plan: `make check`
Differential Revision: D19335226
Pulled By: ltamasi
fbshipit-source-id: 0cc1794bc9892feda1426ed5522a318f3cb1b692
1dd7873e08