tests: re-enable test for undo
tests: re-enable test for undo

aptivate/etherpad-lite,ether/etherpad-lite,joequant/etherpad-lite,ether/etherpad-lite,joequant/etherpad-lite,aptivate/etherpad-lite,storytouch/etherpad-lite,aptivate/etherpad-lite,storytouch/etherpad-lite,joequant/etherpad-lite,storytouch/etherpad-lite,ether/etherpad-lite,joequant/etherpad-lite,aptivate/etherpad-lite