translator: Fix variable collection for gl_DepthRange. This built-in uniform wasn't being collected in VariableInfo.cpp. Also remove the existing workaround for D3D gl_DepthRange collection. BUG=angleproject:991 BUG=478570 Change-Id: Ie254132e37c307323ba9e6e1705d138eea67b520 Reviewed-on: https://chromium-review.googlesource.com/268524 Tested-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Zhenyao Mo <zmo@chromium.org>