inspector: Allow disposing the inspector

We were hiding the inspector when the window
is closed, but that has the side-effect of
keeping references to application windows,
so we would keep them artificially alive,
which can have side-effects.

So, make the inspector go away when closed.

gtk/inspector/window.c

@@ -226,8 +226,6 @@ gtk_inspector_window_init (GtkInspectorWindow *iw)
                                iw,
                                NULL);
 
-  gtk_window_set_hide_on_close (GTK_WINDOW (iw), TRUE);
-
   gtk_window_group_add_window (gtk_window_group_new (), GTK_WINDOW (iw));
 
   extension_point = g_io_extension_point_lookup ("gtk-inspector-page");