cups-filters: Update print/cups-filters to 1.21.5

pkgsrc changes:
- Remove no more needed patch for poppler 0.71.0
- Add a reference to upstream issue regarding (temporary) opvp
  disabled support

Changes:
1.21.5
------
- cups-browsed: We cannot reliably determine whether a CUPS
  queue is temporary, so we apply the procedure to make a
  temporary queue permanent to any unshared queue (Debian bugs
  #910882, #905850, #908604).
- pdftoraster, pdftopdf, pdftoijs, pdftoopvp: Do not use the
  Poppler-specific "GBool", "gFalse", "gTrue" any more, as
  Poppler has switched to standard "bool", "false", "true" in
  version 0.71.0 (Issue #69).

(leot)