i965: Remove upload_gs_state_for_tf.

i965: Remove upload_gs_state_for_tf.

This function only emits a particular case of 3DSTATE_GS. Instead, we can do
that inside genX(upload_gs_state), and later reuse part of that code for
emitting gen4-5 state.

There's the additional benefit of allowing us to remove gen6_gs_state.c, which
was only left because of this function.

Signed-off-by: Rafael Antognolli <rafael.antognolli@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>