Bug 975042 - Remove the special COW support for Date. r=peterv

As soon as Date is on Xrays, this stuff won't work anyway. Henceforth, content
access to chrome Date objects is forbidden, and APIs should use something like
|new contentWindow.Date()| for any Date object they wish to expose to content.

js/src/jsdate.cpp

@@ -3179,19 +3179,3 @@ static const NativeImpl sReadOnlyDateMethods[] = {
     date_toString_impl,
     date_valueOf_impl
 };
-
-JS_FRIEND_API(bool)
-js::IsReadOnlyDateMethod(IsAcceptableThis test, NativeImpl method)
-{
-    /* Avoid a linear search in the common case by checking the |this| test. */
-    if (test != IsDate)
-        return false;
-
-    /* Linear search, comparing function pointers. */
-    unsigned max = sizeof(sReadOnlyDateMethods) / sizeof(sReadOnlyDateMethods[0]);
-    for (unsigned i = 0; i < max; ++i) {
-        if (method == sReadOnlyDateMethods[i])
-            return true;
-    }
-    return false;
-}