Do not create dummy variables when linking uniforms. This cleanup prepares us for removing the uniform register info from the shader translator types. BUG=angle:466 Change-Id: I86f47970b793135f410a5ef698fc96d44219ee96 Reviewed-on: https://chromium-review.googlesource.com/207253 Tested-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Zhenyao Mo <zmo@chromium.org>