i965: Drop INTEL_DEBUG=stats.

i965: Drop INTEL_DEBUG=stats.

For whatever reason, we had an INTEL_DEBUG=stats option that enabled
various statistics counters on Gen4-5 systems.  It's been around
forever, though I can't think of a single time that it's been useful.

On Gen6+, we enable statistics all the time because they're necessary
to support various query object targets.  Turning them off would break
those queries.

Gen4-5 don't support those queries, so the statistics counters generally
aren't useful; we disabled them by default.  This patch disables them
altogether.

Reviewed-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>