Use gtk to detect dpi.

sugar/activity/activity.py

@@ -32,11 +32,6 @@ class Activity(Window, gtk.Container):
     def __init__(self, handle):
         Window.__init__(self)
 
-        # FIXME: This will work only for activities in python. We need a xsetting.
-        display = gtk.gdk.display_manager_get().get_default_display()
-        screen = display.get_default_screen()
-        screen.set_resolution(_sugar.get_screen_dpi())
-
         self.connect('destroy', self._destroy_cb)
 
         self._shared = False