Remove inaccurate code comment (#6274)

Summary:
Remove a comment.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6274

Differential Revision: D19323151

Pulled By: riversand963

fbshipit-source-id: d0d804d6882edcd94e35544ef45578b32ff1caae

db/internal_stats.cc

@@ -663,7 +663,6 @@ bool InternalStats::HandleNumImmutableMemTableFlushed(uint64_t* value,
 
 bool InternalStats::HandleMemTableFlushPending(uint64_t* value, DBImpl* /*db*/,
                                                Version* /*version*/) {
-  // Return number of mem tables that are ready to flush (made immutable)
   *value = (cfd_->imm()->IsFlushPending() ? 1 : 0);
   return true;
 }