iris: Stop setting up fake params

iris: Stop setting up fake params

In d1c4e64a69e, we added a parameter to tell the back-end compiler to
ignore the param array and just push however many constants you ask it
to push.  Iris doesn't want to push anything so it gives a bogus number
of parameters and trusts the back-end compiler to dead-code all of them.
Now that we can tell the back-end compiler to stop re-arranging things,
delete the hack and enable the new simpler code path.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>