The ErrorOrResult pattern doesn't help much. Removing it enables the
Error passing refactor in the Vulkan back-end.

Bug: angleproject:2713
Change-Id: I4e8277ad856c785bf22b4d37b7ae880b534ef005
Reviewed-on: https://chromium-review.googlesource.com/1128919
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Frank Henigman <fjhenigman@chromium.org>