Remove the threadframe stuff which went unused.

shell/sugar-shell

@@ -28,7 +28,6 @@ import gobject
 from sugar import logger
 from sugar import profile
 from sugar import env
-from sugar import TracebackUtils
 
 logger.cleanup()
 logger.start('shell')
@@ -86,11 +85,9 @@ model = ShellModel()
 service = ShellService(model)
 shell = Shell(model)
 
-tbh = TracebackUtils.TracebackHelper()
 try:
 	gtk.main()
 except KeyboardInterrupt:
 	print 'Ctrl+C pressed, exiting...'
-del tbh
 
 os.remove(dsba_file)