Now that Chromium is switched over, we can remove the old global
APIs so they no longer conflict with glslang/Vulkan.

BUG=angleproject:1319

Change-Id: Ia673d47caa7ca40139e4989fac374acd48f52ab9
Reviewed-on: https://chromium-review.googlesource.com/408517Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>