modifiers: Remove sampler-view tests
When a particular modifier is forced, it is not always possible to do various format casts. Normally the gl driver would internally demote the modifier, but this isn't possible with imported buffers with a particular modifier forced.
Perhaps this is a spec issue, but since it is impossible in some cases, lets just remove the tests. The alternative would be to somehow maintain an allow list of which format casts are permitted for a given modifier, which doesn't seem reasonable.
fwiw, https://gitlab.freedesktop.org/mesa/mesa/-/blob/main/src/gallium/drivers/freedreno/a6xx/fd6_resource.cc?ref_type=heads#L137 gives an idea of what is possible and not for DRM_FORMAT_MOD_QCOM_COMPRESSED .. I expect other hw has their own constraints.