CRM-8338 removed CRM_Contact_Form_Task_Label::mergeSameHousehold(), made obsolete by CRM_Contact_Form_Task::mergeContactIdsByHousehold() implemented in previous commit.

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* CRM-8338: Mailing Label Household Merge requires Household to be selected as well as individuals
  http://issues.civicrm.org/jira/browse/CRM-8338