i965/vec4: Delete the system value infastructure

The only thing still using it is INVOCATION_ID for geometry shaders.
That's easily enough inlined into the nir_intrinsic_load_invocation_id
handling code.

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

src/intel/compiler/brw_vec4_tcs.h

@@ -49,8 +49,6 @@ public:
                     const struct brw_vue_map *input_vue_map);
 
 protected:
-   virtual dst_reg *make_reg_for_system_value(int location);
-   virtual void nir_setup_system_value_intrinsic(nir_intrinsic_instr *instr);
    virtual void setup_payload();
    virtual void emit_prolog();
    virtual void emit_thread_end();