Don't link against MetalKit when building the base Skia library.

MetalKit was introduced in iOS 9 and contains utilities for building
applications with Metal. None of these utilities actually seem to be in use.
However, linking against MetalKit means Flutter cannot deploy a unified binary
to iOS 8. This patch removes the unused dependency and unblocks Flutter.

Fixes https://github.com/flutter/flutter/issues/64017

Change-Id: I2cf54a1c95b4c3cda96300861598f2cb23f583d6
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/314539
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Xiao Yu <xster@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
1 file changed