proftpd-mod-geoip contains a broken postrm script that deletes a file
on upgrades after the new package has been unpacked. #726742
This can be triggered by either upgrades from wheezy to jessie or
simply
in wheezy by the sequence
install proftpd-mod-geoip
remove (but don't purge) proftpd-mod-geoip
install proftpd-mod-geoip
The proposed fix is to add a preinst script that deletes the broken
script *before* the new package gets unpacked.
Deleting is a safe solution because this is the only command in the
file, the #DEBHELPER# token was expanded to the empty string.