GLES1/Vulkan: Don't validate SPIR-V as VVL does the same Improves TexCombine runtime by ~15%. Bug: angleproject:6644 Change-Id: I01f580fef0caa91ebf600cfc0bbbeca1aa20eb06 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3926037 Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Cody Northrop <cnorthrop@google.com>