Vulkan: Remove redundant vk prefixes in vk_helpers. Cleanup/refactoring only. Bug: angleproject:4911 Change-Id: I4fe06a86a6ecaafa16fd900b6f6229f09ab56a9f Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2334092 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>