[doc] Fix option_*() migration commands in doc The function signature in the doc is not the same as in the code. Also option_removed should probably be removed from the doc since the function in migration.py is empty

#!/bin/sh -e

if [ "$1" = "purge" ] ; then
        rm -rf /etc/cubicweb.d/
        rm -rf /var/log/cubicweb/
        rm -rf /var/lib/cubicweb/
fi

#DEBHELPER#
 
exit 0