bug 736978 - remove JS_FinalizeStub. r=:billm

Currently the GC finalizes on the background thread only objects with null
JSClass::finalize. However, this implies that any object that uses
JS_FinalizeStub for the finalizer would be prevented from the background
finalization.

To fix this the patch removes JS_FinalizeStub replacing it with NULL in all
cases when the class has no custom finalizer. For style consistency the patch
also removed the usage of JSCLASS_NO_OPTIONAL_MEMBERS in the static
declarations as the compiler fills the missing fields with null in any cases.

js/src/jsapi-tests/testChromeBuffer.cpp

@@ -13,9 +13,7 @@ JSClass global_class = {
     JS_StrictPropertyStub,
     JS_EnumerateStub,
     JS_ResolveStub,
-    JS_ConvertStub,
-    JS_FinalizeStub,
-    JSCLASS_NO_OPTIONAL_MEMBERS
+    JS_ConvertStub
 };
 
 JS::Anchor<JSObject *> trusted_glob, trusted_fun;