Remove DefaultCompactionFilterFactory.

Summary: DefaultCompactionFilterFactory is not used anymore after recent changes. Remove it.

Test Plan: Just run existing tests.

Reviewers: rven, igor, yhchiang, kradhakrishnan, anthony, IslamAbdelRahman

Reviewed By: IslamAbdelRahman

Subscribers: leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D48699

HISTORY.md

@@ -5,6 +5,7 @@
 * CompactionFilter::Context includes information of Column Family ID
 * The need-compaction hint given by TablePropertiesCollector::NeedCompact() will be persistent and recoverable after DB recovery. This introduces a breaking format change. If you use this experimental feature, including NewCompactOnDeletionCollectorFactory() in the new version, you may not be able to directly downgrade the DB back to version 4.0 or lower.
 * TablePropertiesCollectorFactory::CreateTablePropertiesCollector() now takes an option Context, containing the information of column family ID for the file being written.
+* Remove DefaultCompactionFilterFactory.
 
 ## 4.1.0 (10/8/2015)
 ### New Features

include/rocksdb/compaction_filter.h

@@ -116,20 +116,6 @@ class CompactionFilterFactory {
   virtual const char* Name() const = 0;
 };
 
-// Default implementation of CompactionFilterFactory which does not
-// return any filter
-class DefaultCompactionFilterFactory : public CompactionFilterFactory {
- public:
-  virtual std::unique_ptr<CompactionFilter> CreateCompactionFilter(
-      const CompactionFilter::Context& context) override {
-    return std::unique_ptr<CompactionFilter>(nullptr);
-  }
-
-  virtual const char* Name() const override {
-    return "DefaultCompactionFilterFactory";
-  }
-};
-
 }  // namespace rocksdb
 
 #endif  // STORAGE_ROCKSDB_INCLUDE_COMPACTION_FILTER_H_