Remove incorrect comment
Remove incorrect comment

Summary:
We actually create individual compaction filter from compaction filter factory per sub-compaction in `CompactionJob::ProcessKeyValueCompaction`: https://github.com/facebook/rocksdb/blob/master/db/compaction_job.cc#L742
The comment seems incorrect.
Closes https://github.com/facebook/rocksdb/pull/3288

Differential Revision: D6598455

Pulled By: yiwu-arbug

fbshipit-source-id: a6bc059a9103b87a73ae6ec4bb01ca33f5d48cf5

SunguckLee/RocksDB,SunguckLee/RocksDB,SunguckLee/RocksDB,SunguckLee/RocksDB,SunguckLee/RocksDB,SunguckLee/RocksDB,SunguckLee/RocksDB,SunguckLee/RocksDB