Fix creation of duplicate PostExtraElection objects in tests
Fix creation of duplicate PostExtraElection objects in tests

This fixes an error introduced in 2574243a39d90a2673cf56647c524 - the
PostExtraElection objects *were* being created, because of specifying
the list of elections for the 'elections' kwarg to
PostExtraFactory.create.

DemocracyClub/yournextrepresentative,DemocracyClub/yournextrepresentative,DemocracyClub/yournextrepresentative