8233220: Space::_par_seq_tasks is unused after CMS removal

Reviewed-by: pliden, tschatzl, lkorinth

src/hotspot/share/gc/shared/space.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -69,11 +69,6 @@ class Space: public CHeapObj<mtGC> {
   // Used in support of save_marks()
   HeapWord* _saved_mark_word;
 
-  // A sequential tasks done structure. This supports
-  // parallel GC, where we have threads dynamically
-  // claiming sub-tasks from a larger parallel task.
-  SequentialSubTasksDone _par_seq_tasks;
-
   Space():
     _bottom(NULL), _end(NULL) { }
 
@@ -225,9 +220,6 @@ class Space: public CHeapObj<mtGC> {
   virtual void print_short_on(outputStream* st) const;
 
 
-  // Accessor for parallel sequential tasks.
-  SequentialSubTasksDone* par_seq_tasks() { return &_par_seq_tasks; }
-
   // IF "this" is a ContiguousSpace, return it, else return NULL.
   virtual ContiguousSpace* toContiguousSpace() {
     return NULL;