who: Move back to the utilities package

This was moved to -acct along with the rest of the accounting tools.
While it does work with accounting data, it's also a core Unix tool
that users would expect to be installed without having to install
the whole accounting system.

Move it back to -utilities, which is also where w(1) lives.

MFC after: 1 day
Reviewed by: manu
Differential Revision: https://reviews.freebsd.org/D52653