DisplayGL: remove getDriverVersion It was unused and going forward angle_gpu_info_util will be used instead. BUG=angleproject:1874 Change-Id: I262cc36066aa28805d50f3fc4442b08477f9e24d Reviewed-on: https://chromium-review.googlesource.com/442024 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Corentin Wallez <cwallez@chromium.org>