Vulkan: Remove BufferUtils shader This was the first internal shader written for prototyping UtilsVk. It ended up never having a user. Bug: angleproject:2022 Change-Id: I846dcc216c4c018f5bda16ad67463f698b8e1c56 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2280944 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>