Remove an unused enum.

Change-Id: I792a5a6b890ac37b3e1fa1f3e4a6413b7621d115
diff --git a/vm/alloc/MarkSweep.h b/vm/alloc/MarkSweep.h
index 5323628..5e5a0eb 100644
--- a/vm/alloc/MarkSweep.h
+++ b/vm/alloc/MarkSweep.h
@@ -44,13 +44,6 @@
     const void *finger;   // only used while scanning/recursing.
 } GcMarkContext;
 
-enum RefType {
-    REF_SOFT,
-    REF_WEAK,
-    REF_PHANTOM,
-    REF_WEAKGLOBAL
-};
-
 bool dvmHeapBeginMarkStep(GcMode mode);
 void dvmHeapMarkRootSet(void);
 void dvmHeapScanMarkedObjects(void);