bug#68600: 30.0.50; Bad mode hook docstring when mode-line constructs are present in the mode-name

[Phil Sainty]

> "Hook run after entering ‘example-lisp-mode’."

This is also consistent with the minor mode hook docstring code,
which is doing this:

         (put ',hook 'variable-documentation
              ,(format "Hook run after entering or leaving `%s'.
No problems result if this variable is not bound.
`add-hook' automatically binds it.  (This is true for all hook 
variables.)"
                       modefun))


The sole difference being %S vs %s -- I figure that should be
consistent one way or the other?