8268964: Remove unused ReferenceProcessorAtomicMutator

Reviewed-by: tschatzl, pliden

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

@@ -397,7 +397,6 @@ class ReferenceProcessor : public ReferenceDiscoverer {
 
   // whether discovery is atomic wrt other collectors
   bool discovery_is_atomic() const { return _discovery_is_atomic; }
-  void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; }
 
   // whether discovery is done by multiple threads same-old-timeously
   bool discovery_is_mt() const { return _discovery_is_mt; }
@@ -561,27 +560,6 @@ class ReferenceProcessorIsAliveMutator: StackObj {
   }
 };
 
-// A utility class to temporarily change the disposition
-// of the "discovery_is_atomic" field of the
-// given ReferenceProcessor in the scope that contains it.
-class ReferenceProcessorAtomicMutator: StackObj {
- private:
-  ReferenceProcessor* _rp;
-  bool                _saved_atomic_discovery;
-
- public:
-  ReferenceProcessorAtomicMutator(ReferenceProcessor* rp,
-                                  bool atomic):
-    _rp(rp) {
-    _saved_atomic_discovery = _rp->discovery_is_atomic();
-    _rp->set_atomic_discovery(atomic);
-  }
-
-  ~ReferenceProcessorAtomicMutator() {
-    _rp->set_atomic_discovery(_saved_atomic_discovery);
-  }
-};
-
 enum class RefProcThreadModel { Multi, Single };
 
 /*