Repair and speed up safe-copy-tree and make it internal (bug#61962)

Repair and speed up safe-copy-tree and make it internal (bug#61962)

There is no particular requirement for safe-copy-tree so let's make it
internal for now.  The new implementation is faster and more correct.

* doc/lispref/lists.texi (Building Lists):
* etc/NEWS:  Remove doc and announcement.
* lisp/subr.el (safe-copy-tree--seen, safe-copy-tree--1)
(safe-copy-tree): Remove old version.
* lisp/emacs-lisp/bytecomp.el (bytecomp--copy-tree-seen)
(bytecomp--copy-tree-1, bytecomp--copy-tree): Add new version.
(byte-compile-initial-macro-environment): Use it.
* test/lisp/subr-tests.el (subr--safe-copy-tree):
* test/lisp/emacs-lisp/bytecomp-tests.el (bytecomp--copy-tree):
Move and improve tests.