stop adding custom fields twice in views

Currently Views lists custom field attached to Contacts 2 ways hence they are listed in the "CiviCRM Contacts" group and in individual groups for each groups of Custom fields. The later is preferred as it ensures the field in question passes through the civicrm_views_custom_data_cache() function which does a bunch of work to ensure the correct handler is used.

The former group (CiviCRM Contact) passes custom fields through the less than ideal civicrm_views_add_fields() function which causes issues because the civicrm_views_add_fields() function assigns generic handlers to the fields which is a major issue for and type of multi-select field types such as 'Multi-Select', 'AdvMulti-Select', 'CheckBox', 'Multi-Select Country' and 'Multi-Select State/Province'