* lisp/font-lock.el (font-lock-beginning-of-syntax-function): Remove

(font-lock-fontify-block): Don't let-bind it.
(font-lock-compile-keywords): Don't use it.
(font-lock-set-defaults): Don't set it.  Allow the variable alist to
start one slot earlier, instead.

* lisp/emacs-lisp/syntax.el (font-lock-beginning-of-syntax-function):
Don't declare.
(syntax-ppss): Don't use it either.

* lisp/font-core.el (font-lock-defaults): Remove SYNTAX-BEGIN
from docstring.

* doc/emacs/display.texi (Font Lock): Don't mention
font-lock-beginning-of-syntax-function.

* doc/lispref/modes.texi (Font Lock Basics): Update description of
font-lock-defaults.
(Syntactic Font Lock): Remove font-lock-beginning-of-syntax-function.

* lisp/loadhist.el (unload-feature-special-hooks):
Remove font-lock-beginning-of-syntax-function.

* lisp/obsolete/lazy-lock.el (lazy-lock-fontify-region):
* lisp/emacs-lisp/lisp.el (beginning-of-defun-raw): Don't let-bind
font-lock-beginning-of-syntax-function.

lisp/jit-lock.el

@@ -382,14 +382,6 @@ Defaults to the whole buffer.  END can be out of bounds."
    (save-excursion
      (unless start (setq start (point-min)))
      (setq end (if end (min end (point-max)) (point-max)))
-     ;; This did bind `font-lock-beginning-of-syntax-function' to
-     ;; nil at some point, for an unknown reason.  Don't do this; it
-     ;; can make highlighting slow due to expensive calls to
-     ;; `parse-partial-sexp' in function
-     ;; `font-lock-fontify-syntactically-region'.  Example: paging
-     ;; from the end of a buffer to its start, can do repeated
-     ;; `parse-partial-sexp' starting from `point-min', which can
-     ;; take a long time in a large buffer.
      (let ((orig-start start) next)
        (save-match-data
 	 ;; Fontify chunks beginning at START.  The end of a