Summary:
This option has long been intended to be set to false by default and deprecated. It might never be practical to completely remove the feature, so that we can continue to test for backward compatibility by keeping the ability to generate DBs in the old way.

Also improved API comments.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/11179

Test Plan: existing tests (with one tiny update)

Reviewed By: hx235

Differential Revision: D42973927

Pulled By: pdillinger

fbshipit-source-id: e9bc161cb933266e094aea2dff8cc03753c39dab