Remove parallel sweeping mode, it's no longer used

src/sweeper-thread.cc

 // 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.
 
 #include "src/sweeper-thread.h"
 
 #include "src/v8.h"
 
 #include "src/isolate.h"
 #include "src/v8threads.h"
@@ skipping 58 matching lines @@
 bool SweeperThread::SweepingCompleted() {
   bool value = end_sweeping_semaphore_.WaitFor(base::TimeDelta::FromSeconds(0));
   if (value) {
     end_sweeping_semaphore_.Signal();
   }
   return value;
 }
 
 
 int SweeperThread::NumberOfThreads(int max_available) {
-  if (!FLAG_concurrent_sweeping && !FLAG_parallel_sweeping) return 0;
+  if (!FLAG_concurrent_sweeping) return 0;
   if (FLAG_sweeper_threads > 0) return FLAG_sweeper_threads;
-  if (FLAG_concurrent_sweeping) return max_available - 1;
-  ASSERT(FLAG_parallel_sweeping);
-  return max_available;
+  return max_available - 1;
 }
 
 } }  // namespace v8::internal