This disables forceCpuPathForCubeMapCopy as well

Bug: angleproject:2822
Bug: angleproject:3055
Change-Id: Iecb37d0c2d109e319c67310dd64ad8d4bbc14fd8
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2594707
Commit-Queue: Jie A Chen <jie.a.chen@intel.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>