Delete fast-lock.el and lazy-lock.el

Delete fast-lock.el and lazy-lock.el

The 'font-lock-support-mode' is occasionally useful for debugging
purposes, so it remains as a defvar.
Ref: https://lists.gnu.org/r/emacs-devel/2020-08/msg00125.html

* lisp/obsolete/fast-lock.el:
* lisp/obsolete/lazy-lock.el: Delete libraries obsolete since
22.1.  (Bug#56560)

* lisp/font-lock.el (font-lock-support-mode): Make into a defvar and
delete any mention of 'lazy-lock-mode' and 'fast-lock-mode'.
(font-lock-turn-on-thing-lock, font-lock-turn-off-thing-lock):
Drop support for obsolete modes lazy-lock and fast-lock.
(font-lock-after-fontify-buffer)
(font-lock-after-unfontify-buffer): Make into obsolete function
aliases for 'ignore'.  Adjust callers.
(font-lock-keywords, font-lock-inhibit-thing-lock): Adjust
documentation to not mention lazy-lock and fast-lock.
* lisp/font-core.el (font-lock-defaults): Adjust documentation to
not mention 'font-lock-inhibit-thing-lock'.
* lisp/mail/rmail.el (rmail-variables): Don't inhibit obsolete
lazy-lock-mode and fast-lock-mode.