Toggle SparkMenuButton opened state without delay.

review @devoncarew 

This removes noticeable delay / sluggishness after click to open / close menus.
I have tested it manually in CDE.
I suspect that removing this breaks the functionality. The button should become deactivated when the menu overlay gets auto-closed, e.g. when the mouse is clicked outside of it, when a menu item is selected with the mouse or ENTER, or when it's closed with ESC. I think that even if the code works right now with this removed, that's because of indirect side-effects. E.g. when a menu item is selected, it opens a dialog, which gets focused and thus triggers an `on-blur` for the menu button.

What was the motivation for removing this?