PIDL (DCERPC mapi): enhance dissector

Correctly regenerate mapi dissector (launch via make in pidl/mapi folder)

* Fix -Wunused-variable (fix in request/response.cnf files)
* Fix trailing whitespace

Not yet ready to remove from DIRTY list (there is always some warning about unused tree)

Change-Id: I9759202e320e90f0cb91db5c7dd9650ff62bbadd
Reviewed-on: https://code.wireshark.org/review/4347
Reviewed-by: Anders Broman <a.broman58@gmail.com>