Remove an "unused" variable

Summary:
PR 2893 introduced a variable that is only used in TEST_SYNC_POINT_CALLBACK. When RocksDB is not built in debug mode, this method is not compiled in, and the variable is unused, which triggers a compiler error.

This patch reverts the corresponding part of #2893.
Closes https://github.com/facebook/rocksdb/pull/2956

Reviewed By: yiwu-arbug

Differential Revision: D5955679

Pulled By: asandryh

fbshipit-source-id: ac4a8e85b22da7f02efb117cd2e4a6e07ba73390

db/compaction_job.cc

@@ -1260,9 +1260,11 @@ Status CompactionJob::OpenCompactionOutputFile(
 #endif  // !ROCKSDB_LITE
   // Make the output file
   unique_ptr<WritableFile> writable_file;
+#ifndef NDEBUG
   bool syncpoint_arg = env_options_.use_direct_writes;
   TEST_SYNC_POINT_CALLBACK("CompactionJob::OpenCompactionOutputFile",
                            &syncpoint_arg);
+#endif
   Status s = NewWritableFile(env_, fname, &writable_file, env_options_);
   if (!s.ok()) {
     ROCKS_LOG_ERROR(