(#17448/#17449/#18045) Update fileserver.conf and auth.conf examples

These files still referred to the regime whereby access control lived in
both files and auth.conf usually delegated to fileserver.conf, except
when it didn't. In the meantime, we've improved auth.conf and partially
broken fileserver.conf, and in conversations with the core team, it's
become clear that we don't necessarily WANT to fix fileserver.conf,
especially if not doing so will lead to better and more centralized
access control.

Unfortunately, an awkward period seems unavoidable. This commit
attempts to describe what users SHOULD do and give enough hints that it
will be easy to do so, at the cost of a certain windiness.

NOTE ESPECIALLY that we're now using the word "deprecated," as the
warnings-and-prefs-based deprecation plan outlined at #18045 has been accepted.
Maint: Improve example tagmail.conf file with comments
Maint: Remove example puppet-queue.conf file

This was not a Puppet configuration file; it was a stompserver config
file for use with puppetqd. Which is to say, it was a config file for a
third-party non-production-quality toy backend for a deprecated feature.
I am very sure that we don't need to keep it in the codebase.