Introduce `term-file-aliases', replacing some small lisp/term files

Introduce `term-file-aliases', replacing some small lisp/term files

* lisp/faces.el (term-file-aliases): New variable.
(tty-run-terminal-initialization): Respect term-file-aliases.

* lisp/term/apollo.el, lisp/term/vt102.el, lisp/term/vt125.el:
* lisp/term/vt201.el, lisp/term/vt220.el, lisp/term/vt240.el:
* lisp/term/vt300.el, lisp/term/vt320.el, lisp/term/vt400.el:
* lisp/term/vt420.el: Remove files, replaced by aliases.

* lisp/term/README: Mention term-file-aliases.

* lisp/term/AT386.el, lisp/term/news.el, lisp/term/tvi970.el:
* lisp/term/vt100.el, lisp/term/wyse50.el: Remove obsolete comment.

* doc/emacs/custom.texi (Terminal Init): Mention term-file-aliases.

* doc/lispref/os.texi (Terminal-Specific): Mention term-file-aliases.

* etc/NEWS: Mention this.