Remove scroll listener on destroy so we don’t call undefined onScroll

/cc @izuzak because no PR, @as-cii because this fixes an unexpected
issue with your change.

src/scrollbar-component.coffee

@@ -13,6 +13,7 @@ class ScrollbarComponent
     @domNode.addEventListener 'scroll', @onScrollCallback
 
   destroy: ->
+    @domNode.removeEventListener 'scroll', @onScrollCallback
     @onScroll = null
 
   getDomNode: ->