viewers: Add explicit API for removing display from parent

Previously we were hacking it in

virtManager/console.py

@@ -499,15 +499,11 @@ class vmmConsolePages(vmmGObjectUI):
         if self._viewer is None:
             return
 
-        viewer = self._viewer
-        display = getattr(viewer, "_display")
+        self._viewer.console_remove_display_from_widget(
+            self.widget("console-gfx-viewport"))
+        self._viewer.cleanup()
         self._viewer = None
 
-        viewport = self.widget("console-gfx-viewport")
-        if display and display in viewport.get_children():
-            viewport.remove(display)
-
-        viewer.cleanup()
         self._viewer_is_connected = False
         self._refresh_can_fullscreen()
         self._leave_fullscreen()

virtManager/viewers.py

@@ -249,6 +249,10 @@ class Viewer(vmmGObject):
     def console_has_agent(self):
         return self._has_agent()
 
+    def console_remove_display_from_widget(self, widget):
+        if self._display and self._display in widget.get_children():
+            widget.remove(self._display)
+
 
 ####################
 # VNC viewer class #