Vulkan: Fix the issue with unused attributes / varyings When an attribute, a uniform or a varying isn't used, we now remove their layout and in/out qualifiers so that the shader can still refer to these var names. Bug: angleproject:2456 Change-Id: I5f1241d91bd46f663750adfab2562ef87ce69ae5 Reviewed-on: https://chromium-review.googlesource.com/1014009 Commit-Queue: Luc Ferron <lucferron@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org>