net/openrsync: Improve port

- Fix warnings from portclippy.
- Adjust whitespaces: allign values in LICENSE* variables, remove/add
  several empty lines.
- Remove GNU_CONFIGURE_MANPREFIX.
- Use "${DISTVERSION:S/./-/g}" in GH_TAGNAME instead of hardcoded
  version "1-4-2".
- Use ${PORTNAME} instead of "opendmarc" in GH_TAGNAME and USE_RC_SUBR.

PR:		286588
Approved by:	Dan Mahoney <freebsd@gushi.org> (maintainer)