lib: Remove ancient SCCS tags.

Remove ancient SCCS tags from the tree, automated scripting, with two
minor fixup to keep things compiling. All the common forms in the tree
were removed with a perl script.

Sponsored by: Netflix

Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

Use __SCSSID() for SCCS IDs.

While here, fix $FreeBSD$ ID in ftime.c to use __FBSDID instead of a static
array.

General further adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 3-Clause license.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.

Special thanks to Wind River for providing access to "The Duke of
Highlander" tool: an older (2014) run over FreeBSD tree was useful as a
starting point.

Renumber copyright clause 4

Renumber cluase 4 to 3, per what everybody else did when BSD granted
them permission to remove clause 3. My insistance on keeping the same
numbering for legal reasons is too pedantic, so give up on that point.

Submitted by: Jan Schaumann <jschauma@stevens.edu>
Pull Request: https://github.com/freebsd/freebsd/pull/96

A new jail(8) with a configuration file, to replace the work currently done
by /etc/rc.d/jail.

Trim down libcompat by removing <regexp.h>.

Erwin ran an exp-run with libcompat and <regexp.h> removed. It turns out
the regexp library is almost entirely unused. In fact, it looks like it
is sometimes used by accident. Because these function names clash with
libc's <regex.h>, some application use both <regex.h> and libcompat,
which means they link against the wrong regex library.

This commit removes the regexp library and reimplements re_comp() and
re_exec() using <regex.h>. It seems the grammar of the regular
expressions accepted by these functions is similar to POSIX EREs.

After this commit, 1 low-profile port will be broken, but the maintainer
already has a patch for it sitting in his mailbox.