Metal: Remove MTLGPUFamilyApple9, it is unused Fixes visionOS compiles, the SDKs do not define the symbols. Changes the SDK #if checks to be more consistent: - Remove version checks from WATCHOS, as it's expected to be compiled with fairly recent SDK (Metal is not supported). - Compile fallbacks only when needed by the minimum deployment target. - Add Apple3 -> :MTLFeatureSet_tvOS_GPUFamily2_v1 mapping just for consistency. Bug: angleproject:347739670 Change-Id: I054c9faeba4245be8be6cfa7128f17df03f448da Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5771352 Auto-Submit: Kimmo Kinnunen <kkinnunen@apple.com> Commit-Queue: Kimmo Kinnunen <kkinnunen@apple.com> Commit-Queue: Geoff Lang <geofflang@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Alexey Knyazev <lexa.knyazev@gmail.com>