Change remaining compile-time folding errors to warnings The GLES working group has decided to amend the spec so that implementations are not allowed to generate compile errors on undefined values detected at compile time. Change the remaining folding errors to warnings to follow the newly clarified rules. The end2end_tests covering this are removed, since they're redundant with the more efficient unit test. BUG=angleproject:1703 TEST=angle_unittests Change-Id: I97d2fd532dbe5733581bdc4aa40a5d7d3734fc0d Reviewed-on: https://chromium-review.googlesource.com/427799 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>