Summary:
Various renaming and fixes to get rid of remaining uses of
"backupable" which is terminology leftover from the original, flawed
design of BackupableDB. Now any DB can be backed up, using BackupEngine.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9792
Test Plan: CI
Reviewed By: ajkr
Differential Revision: D35334386
Pulled By: pdillinger
fbshipit-source-id: 2108a42b4575c8cccdfd791c549aae93ec2f3329
Peter Dillinger