Remove unused StubType's, freeing 2 bits in Code objects.

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 6cb5e212026de06051e8d83d9000964d4e3a7ba5..e5badbc83450193cd404900a521091e775e40948 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -11075,12 +11075,7 @@ const char* Code::ICState2String(InlineCacheState state) {
 const char* Code::StubType2String(StubType type) {
   switch (type) {
     case NORMAL: return "NORMAL";
-    case FIELD: return "FIELD";
-    case CONSTANT: return "CONSTANT";
-    case CALLBACKS: return "CALLBACKS";
-    case INTERCEPTOR: return "INTERCEPTOR";
-    case TRANSITION: return "TRANSITION";
-    case NONEXISTENT: return "NONEXISTENT";
+    case FAST: return "FAST";
   }
   UNREACHABLE();  // keep the compiler happy
   return NULL;