Clean up Handle<> comparison with null.

These operators do not need the mutator lock.

Test: buildbot-build.sh
Change-Id: I48f51853f1b3c2e56463140f23777ad26d8122f2
diff --git a/compiler/optimizing/nodes.h b/compiler/optimizing/nodes.h
index 48dae87..939c49f 100644
--- a/compiler/optimizing/nodes.h
+++ b/compiler/optimizing/nodes.h
@@ -6833,7 +6833,7 @@
   }
 
   // Loaded class RTI is marked as valid by RTP if the klass_ is admissible.
-  void SetValidLoadedClassRTI() REQUIRES_SHARED(Locks::mutator_lock_) {
+  void SetValidLoadedClassRTI() {
     DCHECK(klass_ != nullptr);
     SetPackedFlag<kFlagValidLoadedClassRTI>(true);
   }
@@ -7696,7 +7696,7 @@
   }
 
   // Target class RTI is marked as valid by RTP if the klass_ is admissible.
-  void SetValidTargetClassRTI() REQUIRES_SHARED(Locks::mutator_lock_) {
+  void SetValidTargetClassRTI() {
     DCHECK(klass_ != nullptr);
     SetPackedFlag<kFlagValidTargetClassRTI>(true);
   }