panfrost/midgard: Don't assign var locations ourselves

panfrost/midgard: Don't assign var locations ourselves

This piece of code was cargo-culted from the ir3 standalone compiler and
made sense when we were a standalone compiler ourselves. Unfortunately,
for the online compiler, mesa/st *already handles this for us* and if we
duplicate it here, we're duplicating it *incorrectly*. So just delete
these lines and fix a heck of a lot of tests.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>