Apply the last step of the new way to update the link-layer header length

Apply the last step of the new way to update the link-layer header length

All the link-layer dissectors are now void functions.

All the functions were moved to the void_printers[] array.
Rename this array to printers[].
Remove the uint_printers[] array, now empty.
Remove the 'ndo_void_printer' flag field, now useless, from
netdissect_options.
Remove other transitional code.