Metal: Remove references to xfbActiveUnpaused uniform Metal chooses a shader with or without support for transformfeedback so there's no point in checking in the shader if it's enabled or not. Bug: angleproject:6823 Change-Id: Iacd26b1e55b311a7cc7987dcd8b2f8c0c8727d62 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3343179 Reviewed-by: Kenneth Russell <kbr@chromium.org> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Gregg Tavares <gman@chromium.org>