Usage of SH_DONT_REMOVE_INVARIANT_FOR_FRAGMENT_INPUT is removed from
ANGLE by [1], and from the validating command decoder by [2].  The flag
is only ever disabled in Firefox.

SH_REMOVE_POW_WITH_CONSTANT_EXPONENT is removed from the validating
command decoder by [3].  Not used in Firefox.

[1]: https://chromium-review.googlesource.com/c/angle/angle/+/1558678
[2]: https://chromium-review.googlesource.com/c/chromium/src/+/2810880
[3]: https://chromium-review.googlesource.com/c/chromium/src/+/2810879

Bug: angleproject:4889
Change-Id: If7d9c31c48510b1486a2285a88475b3c01a77527
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2810806Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>