test: don't truncate the final journal

This is no longer necessary, as the test for which this was introduced
in the first place has this handled explicitly (testsuite-04.journal.sh).

Follow-up to 9457dd8bae.

test/units/testsuite-04.sh

@@ -3,9 +3,6 @@
 set -eux
 set -o pipefail
 
-# Limit the maximum journal size
-trap "journalctl --rotate --vacuum-size=20M" EXIT
-
 # shellcheck source=test/units/test-control.sh
 . "$(dirname "$0")"/test-control.sh