Add back renamed function 'font-lock-fontify-syntactically-region'

Add back renamed function 'font-lock-fontify-syntactically-region'

A more accurate replacement for font-lock-fontify-syntactically-region
would be a function that funcalls the
font-lock-fontify-syntactically-function variable. That way, callers
of the function can inherit new behavior, if the value of that variable
changes.

* lisp/font-lock.el (font-lock-fontify-syntactically-region):
Add function back, remove its obsolete alias.

Copyright-paperwork-exempt: yes