Skip the GLES 3.2 context creation by overriding tes31Context.cpp
with an ANGLE-specific tes31Context_override.cpp that only creates a
GLES 3.1 context.

Bug: angleproject:3687
Test: dEQP.GLES31
Change-Id: I1afab5f04b79dc252f1b27563032a44ab37cacfe
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1698542Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Tim Van Patten <timvp@google.com>