Revert D28177176: [iOS GPU] Add Metal API availability check
Test Plan: revert-hammer
Differential Revision:
D28177176 (https://github.com/pytorch/pytorch/commit/30c96c9419f300708496507ff7a71a1918354321)
Original commit changeset: b5913e5ed75d
fbshipit-source-id: e6ea545493b788b66b065a4c16daf31373c9eecc
