[heap][cleanup] Remove unused MarkCompactCollector::DrainMarkingWorklist

Change-Id: I4f3d03ebad41f32eff5d6570ad4d011586f1bac7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3722486
Commit-Queue: Jianxiao Lu <jianxiao.lu@intel.com>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81344}

src/heap/mark-compact.cc

@@ -2307,8 +2307,6 @@ void MarkCompactCollector::PerformWrapperTracing() {
   }
 }
 
-void MarkCompactCollector::DrainMarkingWorklist() { ProcessMarkingWorklist(0); }
-
 template <MarkCompactCollector::MarkingWorklistProcessingMode mode>
 std::pair<size_t, size_t> MarkCompactCollector::ProcessMarkingWorklist(
     size_t bytes_to_process) {

src/heap/mark-compact.h

@@ -615,10 +615,6 @@ class MarkCompactCollector final {
   // otherwise they can die and try to deoptimize the underlying code.
   void ProcessTopOptimizedFrame(ObjectVisitor* visitor, Isolate* isolate);
 
-  // Drains the main thread marking work list. Will mark all pending objects
-  // if no concurrent threads are running.
-  void DrainMarkingWorklist();
-
   // Implements ephemeron semantics: Marks value if key is already reachable.
   // Returns true if value was actually marked.
   bool ProcessEphemeron(HeapObject key, HeapObject value);