r83812, r83814: Don't use cl_type at all when paging categorylinks

r83812, r83814: Don't use cl_type at all when paging categorylinks

* Remove cl_type from paging in categorylinks - it's not
  really needed there. Although cl_type is in WHERE but not
  in ORDER BY clause the worst thing that can happen
  is to have a filesort going again through <500 entries
  selected by index. Or will FORCE INDEX work anyway?

* Revert schema change, as we don't need cl_type there
  anyway (or even if we wanted to compare, it should
  work as expected by using INT values against ENUM).