ART: Move to using locks.h instead of mutex.h

When only annotating lock requirements, use locks.h.

Bug: 119869270
Test: mmma art
Change-Id: I1608b03254712feff0072ebad012c3af0cc3dda4
diff --git a/runtime/gc/reference_processor.h b/runtime/gc/reference_processor.h
index c6c7836..17b546a 100644
--- a/runtime/gc/reference_processor.h
+++ b/runtime/gc/reference_processor.h
@@ -18,7 +18,7 @@
 #define ART_RUNTIME_GC_REFERENCE_PROCESSOR_H_
 
 #include "base/globals.h"
-#include "base/mutex.h"
+#include "base/locks.h"
 #include "jni.h"
 #include "reference_queue.h"