Heads up: lots of churn, nothing interesting will come of it (I hope)

OK. I have pushed 4 series of commits. (1) remove sccs IDs by and large (a
couple of exceptions where @(#) didn't mark an SCCS id). (2) remove if 0'd
copyright strings. (3) Mechanical changes to most of the tree to cleanup
style divots after these changes (and the $FreeBSD$ removal) (4) cdefs.h
cleanups. I also bumped FreeBSD_version. I chunked these a bit differently
than for $FreeBSD$ so any given file will only have 2 or 3 commits rather
than half a dozen. I've done a test MFC and this chunking shouldn't cause
problems, but I've not pushed that since a couple of last second snags
changed most of the hashes, so I have to redo it.

I did all of these all at once so that there'd be only one rebuild for most
people. I plan on doing a MFC to stable/14 (it doesn't look too horrible),
but not to stable/13 unless there's demand. It's too churny, IMHO, for a
branch at that point of maturity.

I tried to triple check everything, and to not delete too much. I did an
exp run on the cdefs changes. All most people will notice is really long
incremental rebuilds....  I hope...

This should be the last wide-scale cleanup like this. There may be some
minor mop of that follows this commit, but there's no more tree-wide
changes on the horizon. I do plan on plowing forward, though, with my
cdefs.h cleanup, though not until after the first of the year.

If my expectations are in error, or you've noticed a mistake in all this,
please let me know.

Warner