Remove superfluous 'virtual' specifiers in ART.

Remove 'virtual' specifier on methods already bearing the 'override'
specifier.

Test: mmma art
Change-Id: I114930969a5ca048d88de9ecd18e2c6403593e31
diff --git a/runtime/monitor.cc b/runtime/monitor.cc
index 6e5786a..72eced2 100644
--- a/runtime/monitor.cc
+++ b/runtime/monitor.cc
@@ -1574,7 +1574,7 @@
  public:
   MonitorDeflateVisitor() : self_(Thread::Current()), deflate_count_(0) {}
 
-  virtual mirror::Object* IsMarked(mirror::Object* object) override
+  mirror::Object* IsMarked(mirror::Object* object) override
       REQUIRES_SHARED(Locks::mutator_lock_) {
     if (Monitor::Deflate(self_, object)) {
       DCHECK_NE(object->GetLockWord(true).GetState(), LockWord::kFatLocked);