Do not use IOSurface copyTexImage2D workaround for LUMA formats.

copyTexImage is implemented for LUMA formats using a blit. Thus, there's no need
to use the copyTexImage2D workaround for IOSurfaces.

BUG=577144, 620067
CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_optional_gpu_tests_rel;tryserver.chromium.mac:mac_optional_gpu_tests_rel;tryserver.chromium.win:win_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2068033002
Cr-Commit-Position: refs/heads/master@{#399825}