anv: Get rid of gen fall-through

anv: Get rid of gen fall-through

In the early days of the Vulkan driver, we thought it would be a good
idea to just make genN just fall back to the genN-1 code if it didn't
need to be any different for genN.  While this seemed like a good idea,
it ultimately ended up being far simpler to just recompile everything.
We haven't been using the fall-through functionality for some time so
we're better off just deleting it so it doesn't accidentally start
causing problems.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>