Summary:
Undo https://github.com/facebook/rocksdb/issues/6243 and fix the crash test failures.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6273

Test Plan: Run make ubsan_crash_test

Differential Revision: D19331472

Pulled By: anand1976

fbshipit-source-id: 30aa4a36c1b0f77a97159d82bbfd1cd767878e28