Vulkan doesn't have a mapping extension to
GL_EXT_robustness, so we need to disable it.

Bug: angleproject:4823
Change-Id: If7b66c0eb7ba14b9349925af64ec2efcec9985a4
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2287092
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>