Drupal views: Remove duplicate relationship on source_record_id

If you create a view based on civicrm activities and add a "Civicrm Source Record Contact" relationship, you will find this relationship doesn't work and anything based off it will return null.

This is because there is a default join already occurring on the column source_record_id to the table civicrm_contact and this relationship is therefore unnecessary.

There are two options. Either delete this relationship entirely or rename the column to an alias and add a 'real field' key to the $data array.

The attached patch prefers the former route (since I can't imagine why you'd need a duplicate join on these tables).