Revert 21780, it does not actually fix the leak in mpi/tests/cache_disable.c, and breaks other tests

mpi/src/starpu_mpi_cache.c

@@ -92,9 +92,6 @@ void _starpu_mpi_cache_shutdown()
 	STARPU_PTHREAD_MUTEX_LOCK(&_cache_mutex);
 	HASH_ITER(hh, _cache_data, entry, tmp)
 	{
-		struct _starpu_mpi_data *mpi_data = entry->data_handle->mpi_data;
-		free(mpi_data->cache_sent);
-		mpi_data->cache_sent = NULL;
 		HASH_DEL(_cache_data, entry);
 		free(entry);
 	}