radv: don't use a separate cache entry for GS copy shaders
This seems simpler and probably faster.
This also fixes a warning for these CTS tests:
dEQP-VK.pipeline.creation_feedback.graphics_tests.vertex_stage_geometry_stage_delayed_destroy_fragment_stage_delayed_destroy
dEQP-VK.pipeline.creation_feedback.graphics_tests.vertex_stage_geometry_stage_fragment_stage
because we no longer set found_in_application_cache=false for pipelines with NGG GS.