It's needlessly complex to query texture info when determining whether
a format is a depth/stencil format. It can be tested simply by
checking if the dsvFormat field of the format set is set.

BUG=angleproject:1244
TEST=angle_end2end_tests,
     dEQP-GLES3.functional.texture.specification.*depth* (no regressions)

Change-Id: I76d008462564657328dae35d664be5f5e22238fa
Reviewed-on: https://chromium-review.googlesource.com/329104Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>