Remove etc/rc.d/mrouted

mrouted has been available in ports for the last 8 years as net/mrouted . An
equivalent rc.d script has been present in the port.

Remove all corresponding variables from etc/defaults/rc.conf

Relnotes: yes


git-svn-id: svn+ssh://svn.freebsd.org/base/head@275299 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f