net/xrdp: Fix build with audio/fdk-aac 2.0.0 etc

Submitter's patch has been merged into upstream with minor changes.

Also while here, cleanup some leftovers. This port generates private key
and server certificate in post-install script. Poudriere complains that
these files are left over after deinstall. Now these auto-generated files
will be removed when deinstall. If certificate and private key are replaced
with user's own files, they should be kept.

PR: 233558
Submitted by: takefu@airport.fm (original version)
Approved by: mentors (implicit)
Obtained from: https://github.com/neutrinolabs/xrdp/pull/1257
Sponsored by: HAW International, Inc.