Detach separable shaders This effectively reverts the following CL: Vulkan: Don't detach separable shaders in Program::detachShader() https://chromium-review.googlesource.com/c/angle/angle/+/2084399 Bug: angleproject:3570 Bug: b/182409935 Test: ProgramPipelineTest31.DetachAndModifyShader Change-Id: Id69f732d1d4f3eea70b2de8c008452878eaf1682 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2776267 Commit-Queue: Tim Van Patten <timvp@google.com> Reviewed-by: Cody Northrop <cnorthrop@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org>