Change alt_callback for cached comms into single cb + flag.

Avoid multi callback parralel paths.

mpi/src/mpi_failure_tolerance/starpu_mpi_checkpoint.c

@@ -121,14 +121,6 @@ void _send_cp_internal_data_cb(void* _args) {
 	_starpu_mpi_push_cp_ack_recv_cb(arg);
 }
 
-void _send_cached_cp_internal_data_cb(void* _args)
-{
-	struct _starpu_mpi_cp_ack_arg_cb* arg = (struct _starpu_mpi_cp_ack_arg_cb*) _args;
-	starpu_data_release(arg->handle);
-	_starpu_mpi_push_cp_ack_recv_cb(arg);
-}
-
-
 int starpu_mpi_submit_checkpoint_template(starpu_mpi_checkpoint_template_t cp_template)
 {
 	starpu_data_handle_t handle;