Deprecate and Disable non-deferred and non-postproc rendering

Non-Postproc and Non-Deferred rendering behave visually subtly different in a lot of ways beyond what is expected (such as fog distanced being different between the deferred and forward rendering).

Since almost all work is done in deferred + postproc these days, and the other options are just hanging on life support and should not be used by anyone anymore.

As such, we should just eventually fully disable them so that we can start ripping out old compat bits that are no longer used and cause maintenance overhead.