HEADS UP: $FreeBSD$ Removed from main

Greetings,

I've just pushed the results that remove 31,035 instances of $FreeBSD$ from
the main branch.

From this point out, we are effectively done with $FreeBSD$, though there's
4 places where $FreeBSD$ still exists in the tree:
(1) In the contrib area, we have 621 remaining. I didn't remove any from
contrib code.
(2) There's 140 $FreeBSD$ or similar tags part of 'static const char
rcsid[] = "$FreeBSD$". There's too many different styles to get with
automation, and they are also intertwingled with sccsid[] entries, other
SCCS tags and copyright strings. These will be sorted out separately, since
we need to talk about old sccs tags in the tree and sort that out too at
the same time.
(3) There's one $FreeBSD$ in a version tag for bootinfo for chrp
bootinfo.txt. I don't know the effects of removing this entry, so I left it
in place. Not sure it's worth fixing.
(4) indent tests remove $FreeBSD$ so that it doesn't screw them up. This is
likely harmless, but could be removed. I didn't want to mess with it,
though.

I've removed 99.5%+ of the 'live' instances in the tree. The ones from
contrib should be removed upstream and

I plan to do a MFC-like thing where I cherry-pick some commits, and run my
script against stable/13 and include the main hash so our scripting things
it's a real MFC (the diff hashes will differ, so git's native tooling will
take the slow path, at least, and may get confused otherwise.

I've built world on aarch64 and amd64. I've built kernels on all the
architectures after this change... or well, last night's main. I eye-balled
today's changes and they all look good, but there's no incremental building
with this change, so I'm starting a new universe after I loop the change
back into my tree. Also: expect long build times, git fetch times, etc
after this.

Thanks to the many people who gave me feedback on the details of this
change and how to chunk it up. Hopefully the 40ish commits was the right
balance between 'all at once' and 'every dir'.

As always, if there's any problems after this change, please let me know.

Warner