test: Actually run cleanup function

We install a cleanup() function with 'trap' in order to clean up temporary
files we generate during the tests.  However, we deinstall it after
run_term, which means it won't run in most of the cases where it would be
useful.  Even if "run from_term" exits with an error, that error will be
hidden from the run_term wrapper because it's within a tmux session, so we
will return from run_term normally, uninstall the trap and never clean up.

In fact there's no reason to uninstall the trap at all, it works just as
well on the success exit path as an error exit path.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

test/run

@@ -178,7 +178,6 @@ else
 	:> "${LOGFILE}"
 	trap "cleanup" EXIT
 	run_term
-	trap "" EXIT
 fi
 
 [ ${DEMO} -eq 1 ] && exit 0