* lisp/progmodes/which-func.el: Improve disabling the mode

* lisp/progmodes/which-func.el: Improve disabling the mode

Use lexical-binding.
(which-func-modes, which-func-non-auto-modes, which-func-maxout)
(which-func, which-func-format): Remove redundant :group arg.
(which-func-try-to-enable): New function.
(which-func-ff-hook, which-function-mode): Use it.
(mode-line-misc-info): Add ourselves here instead of in bindings.el.
* lisp/bindings.el (mode-line-misc-info): Remove which-func-mode entry.