Removes ash::features::ShouldUseShaderRoundedCorner() feature

This has been enabled on all devices for a while, now we can say
it's always true. Removing the flag and the legacy code now
makes sense.

Bug: 979365
Test: compilation succeeds / trybot
Change-Id: Icf8bbf06fbd385ad9ff50380d242e0b4b43960e2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1680986
Commit-Queue: Jun Mukai <mukai@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Reviewed-by: Malay Keshav <malaykeshav@chromium.org>
Cr-Commit-Position: refs/heads/master@{#673408}
29 files changed