selftests: mptcp: connect: remove unused variable

'cin_disconnect' is used in run_tests_disconnect(), but not
'cout_disconnect', so it is safe to drop it.

Reviewed-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20250114-net-next-mptcp-st-more-debug-err-v1-5-2ffb16a6cf35@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/net/mptcp/mptcp_connect.sh

@@ -137,7 +137,7 @@ TEST_GROUP=""
 #shellcheck disable=SC2317
 cleanup()
 {
-	rm -f "$cin_disconnect" "$cout_disconnect"
+	rm -f "$cin_disconnect"
 	rm -f "$cin" "$cout"
 	rm -f "$sin" "$sout"
 	rm -f "$capout"
@@ -155,7 +155,6 @@ cin=$(mktemp)
 cout=$(mktemp)
 capout=$(mktemp)
 cin_disconnect="$cin".disconnect
-cout_disconnect="$cout".disconnect
 trap cleanup EXIT
 
 mptcp_lib_ns_init ns1 ns2 ns3 ns4