move the SunOS r-commands into the rcmds package

rup, rusers and rwall implement the SunOS remote status utilities based
on RPC. these are not widely used nowadays and most users won't have
them enabled, so there's no reason to ship them in the utilities
packages.

move the command-line utilities and their respective daemons into the
rcmds package, which already contains the related utilities rwho and
ruptime.

improve the comment/description of the rcmds package to be more
informative and mention its new contents.

while here, standardise formatting in the affected Makefiles.

Reviewed by: manu, imp, des, emaste
Approved by: des (mentor)
Differential Revision: https://reviews.freebsd.org/D50143