Remove extra ] configure.ac for HAVE_DETECT_DISABLED

Saw a warning about unknow command ']' running distcheck and tracked it back
to this error.

https://buildbot.suricata-ids.org/builders/ken-tilera/builds/112
- PR pcaps: https://buildbot.suricata-ids.org/builders/ken-tilera-pcap/builds/46
- PR build: https://buildbot.suricata-ids.org/builders/ken-tilera/builds/113