Since this commit was made, dEQP tests were fixed to check that
unrecognized pragma tokens only generate warnings, not errors.

This applies to both ESSL1.00 and ESSL3.00, which specify this
behavior in section 3.4 Preprocessor.

BUG=angleproject:989
TEST=dEQP-GLES2.functional.shaders.preprocessor.pragmas.*

This reverts commit d3c29f57.

Change-Id: Ie4e0ec061fa3164d6f3872ac0016a063056ed110
Reviewed-on: https://chromium-review.googlesource.com/293181Tested-by: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>