refactor(sidebar): remove un-used legacy code

This removes the duration property from the default settings.

It was used for legacy animation mode (jquery instead of css), but that feature was removed a long time ago (2229306)

Author: ColinFrick

src/definitions/modules/sidebar.js

@@ -1063,8 +1063,6 @@ $.fn.sidebar.settings = {
   returnScroll      : false,
   delaySetup        : false,
 
-  duration          : 500,
-
   onChange          : function(){},
   onShow            : function(){},
   onHide            : function(){},