[Metal] Remove unused shader code (#73636)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/73636
Clean up unused shader code for supporting iOS 10.0 to save some code size.
ghstack-source-id: 150591224
Test Plan: Sandcastle
Reviewed By: dhruvbird
Differential Revision: D34571726
fbshipit-source-id: 47e678f14c3368f54afa707fa1fd797b03ef950b
(cherry picked from commit 7d120cc89b3a919afec58ced798dcce39b17f362)
