i965/vec4: Use NIR to do GS input remapping

We're already doing this in the FS back-end.  This just does the same
thing in the vec4 back-end.

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/intel/compiler/gen6_gs_visitor.cpp

@@ -516,9 +516,7 @@ gen6_gs_visitor::setup_payload()
 
    reg = setup_uniforms(reg);
 
-   reg = setup_varying_inputs(reg, attribute_map, attributes_per_reg);
-
-   lower_attributes_to_hw_regs(attribute_map, true);
+   reg = setup_varying_inputs(reg, attributes_per_reg);
 
    this->first_non_payload_grf = reg;
 }