selftests/xsk: Fix double free

Fix a double free at exit of the test suite.

Fixes: a693ff3 ("selftests/xsk: Add support for executing tests on physical device")
Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Link: https://lore.kernel.org/bpf/20220929090133.7869-1-magnus.karlsson@gmail.com

tools/testing/selftests/bpf/xskxceiver.c

@@ -1953,9 +1953,6 @@ int main(int argc, char **argv)
 
 	pkt_stream_delete(tx_pkt_stream_default);
 	pkt_stream_delete(rx_pkt_stream_default);
-	free(ifobj_rx->umem);
-	if (!ifobj_tx->shared_umem)
-		free(ifobj_tx->umem);
 	ifobject_delete(ifobj_tx);
 	ifobject_delete(ifobj_rx);