selftests/net: unix: fix unused variable compiler warning

Remove an unused variable.

    diag_uid.c:151:24:
    error: unused variable 'udr'
    [-Werror,-Wunused-variable]

Fixes: ac011361 ("af_unix: Add test for sock_diag and UDIAG_SHOW_UID.")
Signed-off-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/r/20231124171645.1011043-4-willemdebruijn.kernel@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/net/af_unix/diag_uid.c

@@ -148,7 +148,6 @@ void receive_response(struct __test_metadata *_metadata,
 		.msg_iov = &iov,
 		.msg_iovlen = 1
 	};
-	struct unix_diag_req *udr;
 	struct nlmsghdr *nlh;
 	int ret;