Remove sweeper threads

src/isolate.h

Index: src/isolate.h
diff --git a/src/isolate.h b/src/isolate.h
index 9ea30743bdf56db47473f3197976c778ffac698f..d08ab0c04ecdc561f7c04dadcb7ef8079928d9e1 100644
--- a/src/isolate.h
+++ b/src/isolate.h
@@ -1060,14 +1060,6 @@ class Isolate {
     return optimizing_compiler_thread_;
   }
 
-  int num_sweeper_threads() const {
-    return num_sweeper_threads_;
-  }
-
-  SweeperThread** sweeper_threads() {
-    return sweeper_thread_;
-  }
-
   int id() const { return static_cast<int>(id_); }
 
   HStatistics* GetHStatistics();
@@ -1319,8 +1311,6 @@ class Isolate {
 
   DeferredHandles* deferred_handles_head_;
   OptimizingCompilerThread* optimizing_compiler_thread_;
-  SweeperThread** sweeper_thread_;
-  int num_sweeper_threads_;
 
   // Counts deopt points if deopt_every_n_times is enabled.
   unsigned int stress_deopt_count_;