iris: Drop dead state_size hash table

iris: Drop dead state_size hash table

I inherited this from i965.  It would be nice to track the state size
so INTEL_DEBUG=color,bat decoding can print the right number of e.g.
binding table entries or blend states, but...without a single point
of entry for state, it's a little tricky to get right.  Punt for now,
and drop the dead code in the meantime.