Don't remove a widget from display before actual removal

This change ensures that, for example, the widget remains in the
Screen.focus_chain so that it's easier to handle passing off focus on
removal.

To help address #939.

src/textual/widget.py

@@ -1775,7 +1775,6 @@ class Widget(DOMNode):
 
     def remove(self) -> None:
         """Remove the Widget from the DOM (effectively deleting it)"""
-        self.display = False
         self.app.post_message_no_wait(events.Remove(self, widget=self))
 
     def render(self) -> RenderableType: