This struct was used to implement different views for stencil mode. It
is replaced with a single stencil mode view for sampling.

We shouldn't be using a stencil-specific view for our render view. In
cases where we're attaching a Depth/Stencil texture to a Framebuffer's
special depth/stencil attachment point we will still need to use a
single 'Draw' view attached to depth/stencil. So there's no need for a
separate 'Draw' view for stencil.

Also there's no current support for a separate 'Fetch' view for
stencil textures. There may not be any easy way to trigger this path as
it's only used in seamful cube map emulation and image copy. Seamful
emulation is ES 2.0 only while stencil textures are ES 3.1 so that's
not a possible use. Image copy doesn't seem to be possible either as it
stands right now.

Bug: angleproject:3975
Change-Id: Ic999f9471ea533d1184a364732c569124aa802bf
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1842230
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Cody Northrop <cnorthrop@google.com>