After lengthy debate, the GLES working group recommended that this
should be an error in WebGL, though old specs were not updated. Make
ANGLE follow the WebGL spec and generate an error in this case.

This is a partial revert of the patch which added support for defined
operator generated by macro expansion. The preprocessor unit tests
added by the reverted commit are kept, but their expectations are
changed.

This breaks some dEQP tests that are not in line with the WebGL spec.

BUG=angleproject:1335
TEST=angle_unittests, WebGL conformance tests

Change-Id: I7d8a1d42c61367197f2aed4ca4de9297cc48acfc
Reviewed-on: https://chromium-review.googlesource.com/352471Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>