I know that I could remove it from the filesystem, but I wouldn't.
You can use slapcat -n 0 to export your cn=config database to LDIF. Modify the LDIF for cn=config to no longer reference back-shell, and then reload your cn=config DB using slapadd -n 0.
Personally I'd like to see some sort of offline mode for slapd that allows you to purely edit cn=config over ldapi:/// where slapd only accepts connections from the rootdn, and will only respond to queries against the cn=config DIT.
--Quanah -- Quanah Gibson-Mount Sr. Member of Technical Staff Zimbra, Inc A Division of VMware, Inc. -------------------- Zimbra :: the leader in open source messaging and collaboration