Fix flatten which-key--update advice for toggle functions.

[jeff-phil]

Pass flatten parameter to hercules-hide in order to remove advice for which-key--update when flattened. Otherwise, which-key no longer pops-up after certain events.

For example, using the code from top of README for macrostep-mode being the toggle-funs works great.

Except if hit q in macrostep-mode, the map is toggled off when mode is quit. Then which-key no longer works, due to the override advice for which-key--update not being removed. By passing flatten param from hercules toggle, the hercules hide function removes advice.