This removes the need for the setErrorSet method.
Also update some egl::Error TODO bugs.

Bug: angleproject:2491
Change-Id: I0aba07c4a53b579835a88c3dacae294f752e6b17
Reviewed-on: https://chromium-review.googlesource.com/c/1392393Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>