Metal: Remove ifdefs for primitive topology class MTLPrimitiveTopologyClass availability iOS 12.0, minimum runtime 15.0. Remove the ifdefs. Hardcoding ANGLE_IOS_DEPLOY_TARGET is dangerous, likely it has never been correct. Remove. Should use __IPHONE_OS_VERSION_MIN_REQUIRED. Bug: angleproject:360147118 Change-Id: I43d7a364fa0237af1ee1f546015ae884fc373b15 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5797141 Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Alexey Knyazev <lexa.knyazev@gmail.com> Commit-Queue: Kimmo Kinnunen <kkinnunen@apple.com> Auto-Submit: Kimmo Kinnunen <kkinnunen@apple.com>