fix(ZMI Deletion): Should work now

zmi complained about the missing docstring.
This is a security check in zope when calling methods through the web
When using zmi, deleting something invokes manage_delete...
ttw, then security checks are applied, one is to check for a
non empty docstring. This is why it never should problems in our
tests, we deleted only in plone, where the method gets called
from within python code.
Should fix #14 @jensens