remove unused code

Summary:
fixup 6a541afcc4. This code didn't do anything because (1) `bytes_per_sync` is assigned in `EnvOptions`'s constructor; and (2) `OptimizeForCompactionTableWrite`'s return value was ignored, even though its only purpose is to return something.
Closes https://github.com/facebook/rocksdb/pull/3055

Differential Revision: D6114132

Pulled By: ajkr

fbshipit-source-id: ea4831770930e9cf83518e13eb2e1934d1f5487c

db/db_impl.cc

@@ -574,10 +574,6 @@ Status DBImpl::SetDBOptions(
       env_options_for_compaction_ = env_->OptimizeForCompactionTableWrite(
                                             env_options_for_compaction_,
                                             immutable_db_options_);
-      env_options_for_compaction_.bytes_per_sync
-                                    = mutable_db_options_.bytes_per_sync;
-      env_->OptimizeForCompactionTableWrite(env_options_for_compaction_,
-                                            immutable_db_options_);
       write_thread_.EnterUnbatched(&w, &mutex_);
       if (total_log_size_ > GetMaxTotalWalSize() || wal_changed) {
         Status purge_wal_status = SwitchWAL(&write_context);