This will make it easier to verify changes to integer texture DXGI
formats. Currently the DXGI format info table contains some values
that wouldn't make sense after the integer formats are changed, such
as R32_TYPELESS being recorded as a depth format, and we need to make
sure no code relies on this kind of information to make changing the
table safe.

Includes cleaning up unused depth/stencil offset fields from
DXGIFormatInfo.

BUG=angleproject:1244
TEST=dEQP-GLES3.functional.fbo.blit.*depth*

Change-Id: I0149f28e4c6f961af99ac2f5a656f3fbfe13aee6
Reviewed-on: https://chromium-review.googlesource.com/328964Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>