remove a custom implementation of std::is_reference

googlemock/include/gmock/gmock-more-actions.h

@@ -105,7 +105,7 @@ ACTION_TEMPLATE(SetArgReferee,
   // Ensures that argument #k is a reference.  If you get a compiler
   // error on the next line, you are using SetArgReferee<k>(value) in
   // a mock function whose k-th (0-based) argument is not a reference.
-  GTEST_COMPILE_ASSERT_(internal::is_reference<argk_type>::value,
+  GTEST_COMPILE_ASSERT_(std::is_reference<argk_type>::value,
                         SetArgReferee_must_be_used_with_a_reference_argument);
   ::std::get<k>(args) = value;
 }