Vulkan: Remove vk::ShaderType Use gl::ShaderType instead. For now, only GLES2 shaders are supported in ProgramVk. Bug: angleproject:2522 Change-Id: I17bc9afddb6d39cf45fb4dd37f34c7263a3ed515 Reviewed-on: https://chromium-review.googlesource.com/c/1333970 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>