This change removes the limitation that syncClearState/
syncClearBufferState is only for STANDARD_GL_DESKTOP so that it works on
chromeos.

Test:
conformance2/rendering/clear-srgb-color-buffer.html
deqp/functional/gles3/fbocolorbuffer/clear.html

Bug: chromium:1208297
Change-Id: I7c5fed3545f623cca3f2245c67fddaf3401388b5
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3010630Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jiajia Qin <jiajia.qin@intel.com>