Vulkan: Remove mUse related code from SyncHelperNativeFence Since adding `rx::vk::ExternalFence` class, waiting on `mUse` is almost the same as waiting directly on `mExternalFence`. Because `mUse` is no longer required to release the fence and to reduce code complexity, `mUse` related code paths were removed. Since `SyncHelperNativeFence` no longer using `mUse` no need to inherit from `SyncHelper`. Added `SyncHelperInterface` abstract base instead. Bug: angleproject:8115 Change-Id: I2aabbc905d833f8bf6db36b3be356d6db40349d0 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4392880 Reviewed-by: Charlie Lao <cclao@google.com> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Igor Nazarov <i.nazarov@samsung.com>