VMM/serviceset: Fixed a conditional ProgrammingError.
Affects only setups with Dovecot < v1.2.beta2. Actually the SQL query in
method ServiceSet._load_by_services wasn't updated.
Removed unnecessary code, which would have also produced a
ProgrammingError, if it would have been correct.
.. |curr_vers_rel_date| replace:: The most current version of vmm is 0.6.0,
released on 28 June 2012.
.. |rel_hist| replace:: Older releases are listed in the :doc:`release_history`.