Work around new styles introduced in oojs-ui in I77cd5212c.
Bonus: remove useless styles targeting the dotdotdot popup
in NotificationItemWidget.less: it's not even a popupWidget
any more and it's located in an overlay anyway, so these
styles didn't do anything.
Change-Id: Ifb16b7bb0b01c1eb2551ba4c173042cc759e9b02
