There indeed is no such class in 2.5, but it was removed long before the first 2.5 RC. It only existed in 2.3 and 2.4.
Double-check your classpath, you must be referencing some 2.4 or 2.3 gwt-user.jar. Either that or you're using some third-party library that shadows some UiBinder classes with their own implementations, based on GWT 2.4 or 2.3 (IIRC, GWT-Platform does such a thing for its GinUiBinder
); it might then have manifest during your 2.5RC to 2.5 upgrade because you changed the dependency order in your classpath and pushed gwt-user after the third-party lib.