VCSid removal (#2017)

VCSid removal (#2017)

The libarchive source tree is littered with `__FBSDID("$FreeBSD.*")` and
'$FreeBSD$' tags left over from extracting it from FreeBSD's Subversion
repo. They never made sense for a git repo as git doesn't expand them
and FreeBSD has now removed `$FreeBSD$` from most local source files so
these stand out.

In addition to `__FBSDID` I've removed `__RCSID` which was used once for
a `$NetBSD$` expansion. There might be more of a case to be made for
preserving this one as a diff-reduction measure, but it seems mostly
pointless.

This builds and tests pass except for
libarchive_test_read_disk_directory_traversals which failed on master as
well.