CRM-13388 - Fix upgrade error due to undefined column, "description"

This change allow civicrm_user_categories() to call getModuleUFGroup() without fetching the unused "descripton" column. During an upgrade, civicrm_user_categories() runs before the "description" column is created.

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* CRM-13388: Drush upgrade fails due to missing column, civicrm_uf_group.description
  http://issues.civicrm.org/jira/browse/CRM-13388