PIDL (DCERPC dnsserver): enhance dissector

* Fix -Wunused-function (Add functions to dnsserver.cnf with NOEMIT)
* Remove dissector DCERPC dnsserver from DIRTY list

Change-Id: Id1d4f43784bfbf417156353fd3254375365c35c8
Reviewed-on: https://code.wireshark.org/review/4323
Reviewed-by: Michael Mann <mmann78@netscape.net>