Metal: Remove no longer needed precompiled shaders Bug: angleproject:5186 Change-Id: Ic5a029ba20852843b909cec26517c03eb738bff5 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2482406 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Le Hoang Quyen <le.hoang.q@gmail.com>