Prune 13 obsolete ports

FreeBSD Ports maintainers have already deleted the following:
  audio/gstreamer1-plugins-celt
  devel/netbsd-pkgsrc-mk-files
  devel/p5-IO
  math/p5-MatrixReal
  sysutils/rsyslog6
  sysutils/rsyslog6-dbi
  sysutils/rsyslog6-gnutls
  sysutils/rsyslog6-mysql
  sysutils/rsyslog6-pgsql
  sysutils/rsyslog6-relp
  sysutils/rsyslog6-rfc3195
  sysutils/rsyslog6-snmp
  www/mod_wsgi