idl2wrs (DCERPC): fix some warning

* Fix -Wmissing-prototypes in
* Fix unused variable for drusapi (using _U_)

Need to fix indent and some unused function/variable to remove from DIRTY list

Change-Id: Ib6f325f0b54e2eb254ec38a41199b4b60a4d90a1
Reviewed-on: https://code.wireshark.org/review/4398
Petri-Dish: Anders Broman <a.broman58@gmail.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Anders Broman <a.broman58@gmail.com>