dEQP was inadvertendly requiring the presence of these extensions to
even run the tests. There's a WIP fix to the dEQP tests and this CL
implements that fix as a temporary workaround until we can update dEQP.

Fixes several tests in KHR-GLES31.core.constant_expressions and
KHR-GLES31.core.shader_macros. They now correctly return unsupported.

Bug: angleproject:4143
Change-Id: I110beb2f18fd29f8f02b2ab166cfcfcfae80c2c1
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1924620Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Reviewed-by: Tim Van Patten <timvp@google.com>
Commit-Queue: Jamie Madill <jmadill@chromium.org>