It is not feasible to run dEQP against ES 3.1 on the bots without removing this
assertion.  Messages will still be logged and UNREACHABLE will still generate
assertion failures when the behaviour is needed.  This matches the behaviour
of Chromium's NOTIMPLEMENTED macro.

Remove the ANGLE_TEST_CONFIG macro, it was not doing anything useful anymore.

BUG=angleproject:1442

Change-Id: I76376817a87e1a75ad1a938e1db1d7763e094372
Reviewed-on: https://chromium-review.googlesource.com/406928Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>