Remove unused-but-set variable from objects.cc.

This fixes compilation with newer GCCs.

R=erik.corry@gmail.com

Review URL: https://chromiumcodereview.appspot.com/10568006

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@11838 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

deps/v8/src/objects.cc

@@ -7514,12 +7514,10 @@ MaybeObject* JSObject::OptimizeAsPrototype() {
 
   // Make sure prototypes are fast objects and their maps have the bit set
   // so they remain fast.
-  Map* proto_map = map();
   if (!HasFastProperties()) {
     MaybeObject* new_proto = TransformToFastProperties(0);
     if (new_proto->IsFailure()) return new_proto;
     ASSERT(new_proto == this);
-    proto_map = map();
   }
   return this;
 }