i965: Stop doing our optimization on a copy of the GLSL IR.

i965: Stop doing our optimization on a copy of the GLSL IR.

The original intent was that we'd keep a driver-private copy, and there
would be the normal copy for swrast to make use of without the tuning (or
anything more invasive we might do) specific to i965.  Only, we don't
generate swrast code any more, because swrast can't render current shaders
anyway.  Thus, our private copy is rather a waste, and we can just do our
backend-specific operations on the linked shader.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>