Use 'outline-heading-end-regexp' consistently.

Use 'outline-heading-end-regexp' consistently.

* lisp/outline.el (outline-font-lock-keywords):
For non-nil 'outline-search-function' also search for
'outline-heading-end-regexp' afterwards like there is
'outline-heading-end-regexp' at the end of the regexp counterpart.
(outline-minor-mode-highlight-buffer): Use 'outline-heading-end-regexp'
like in 'outline-font-lock-keywords' instead of "$".
For non-nil 'outline-search-function' also use
'outline-heading-end-regexp' the same way.

* lisp/help.el (describe-bindings): Remove unnecessary
buffer-local 'outline-heading-end-regexp'.

(cherry picked from commit c9cb89edd500e8a142a7e7cc44a4f8335795d038)