Summary:
CLANG complains that passing const to thread is not necessary. The patch removes it form PreparedHeap::Concurrent test.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5443
Differential Revision: D15781598
Pulled By: maysamyabandeh
fbshipit-source-id: 3aceb05d96182fa4726d6d37eed45fd3aac4c016