Remove obsolete WinRT files. These were no longer used in the build. Bug: angleproject:3162 Change-Id: I715bb3e6f14ed8c97523dec5b0b58bf9a89be0f0 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1660716 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>