Remove code paths for invoking the offline Metal compiler We experimented with invoking the Metal shader compiler directly to create cacheable shader libraries but the project did not show useful gains. It is currently all dead code, remove it. Bug: b/391990604 Change-Id: I6d13278d1a27d8b3ae961a0846f31292f2506b23 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6245258 Reviewed-by: Kimmo Kinnunen <kkinnunen@apple.com> Commit-Queue: Geoff Lang <geofflang@chromium.org>