i965: Remove legacy clip plane handling from geometry shaders.
We only support geometry shaders in core profiles, where gl_ClipVertex
doesn't exist. Presumably the even older behavior of clipping to
gl_Position isn't supported either. In fact, GLSL 1.50 page 76 claims:
"The shader must also set all values in gl_ClipDistance that have been
enabled via the OpenGL API, or results are undefined."
So we don't need to handle legacy clipping in geometry shaders. I think
Paul added this back when we were considering supporting the old
GL_ARB_geometry_shader4 extension.
This removes a non-orthagonal state dependency on GS compilation.
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Chris Forbes <chrisf@ijw.co.nz>