Remove some more leftover rlogin man page xrefs

rcmds were removed in r32435 and these three man pages can trivially
drop the references.

There's still a reference in pts.4 because it describes a mode
(TIOCPKT_NOSTOP), and only lists rlogin/rlogind as examples of programs
that use that mode. To update later.

MFC after: 1 week
Sponsored by: The FreeBSD Foundation