Revert of [heap] Add more tasks for parallel compaction

src/heap/mark-compact.h

Index: src/heap/mark-compact.h
diff --git a/src/heap/mark-compact.h b/src/heap/mark-compact.h
index 724650c1c4e01492669f88524cc5ee071cb1b6ae..6558eb2ddebba2b6349c64eb2fbf4f2c9ea40247 100644
--- a/src/heap/mark-compact.h
+++ b/src/heap/mark-compact.h
@@ -709,8 +709,11 @@
 
   void EvacuatePagesInParallel();
 
-  // The number of parallel compaction tasks, including the main thread.
-  int NumberOfParallelCompactionTasks();
+  int NumberOfParallelCompactionTasks() {
+    // TODO(hpayer, mlippautz): Figure out some logic to determine the number
+    // of compaction tasks.
+    return 1;
+  }
 
   void WaitUntilCompactionCompleted();