radv: Replace radv_trap_handler_shader with radv_shader.

radv: Replace radv_trap_handler_shader with radv_shader.

Now that the upload memory is tied to the shader itself, the trap handler
shader no longer needs an additional wrapper.

This is a cleanup to ease introduction of a new shader uploading code path.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21541>