i965: Never enable the GS on Gen6.

i965: Never enable the GS on Gen6.

Prior to Gen6, we use the GS for breaking down quads, quad-strips,
and line loops.  On Gen6, earlier stages already take care of this,
so we never need the GS.

Since this code is likely completely untested, remove it for now.
We can write new code when enabling real geometry shaders.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>