Remove parallel sweeping mode, it's no longer used

src/mark-compact.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_MARK_COMPACT_H_
 #define V8_MARK_COMPACT_H_
 
 #include "src/compiler-intrinsics.h"
 #include "src/spaces.h"
 
@@ skipping 552 matching lines @@
   static inline bool IsMarked(Object* obj);
 
   inline Heap* heap() const { return heap_; }
   inline Isolate* isolate() const;
 
   CodeFlusher* code_flusher() { return code_flusher_; }
   inline bool is_code_flushing_enabled() const { return code_flusher_ != NULL; }
   void EnableCodeFlushing(bool enable);
 
   enum SweeperType {
-    PARALLEL_CONSERVATIVE,
     CONCURRENT_CONSERVATIVE,
     PRECISE
   };
 
   enum SweepingParallelism {
     SWEEP_ON_MAIN_THREAD,
     SWEEP_IN_PARALLEL
   };
 
 #ifdef VERIFY_HEAP
@@ skipping 401 matching lines @@
  private:
   MarkCompactCollector* collector_;
 };
 
 
 const char* AllocationSpaceName(AllocationSpace space);
 
 } }  // namespace v8::internal
 
 #endif  // V8_MARK_COMPACT_H_