GLES1/Vulkan: Remove double SPIR-V validation assertion The SPIR-V transformation is validated on program link because many tests link programs but don't draw with them. This helps catch bugs. However, GLES1 programs are always created right before draw, so the SPIR-V transformer will definitely be run on them. The link-time validation is thus unnecessary. This change disables the latter on GLES1, which cuts down the TexCombine test run time by about 10%. Bug: angleproject:6644 Change-Id: Idb9d229fc08bf746f933fa8924fa67e5426f87a7 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3926036 Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Cody Northrop <cnorthrop@google.com>