Bradley Cooper constricts his mobility in unmoving "Elephant Man"
NEW YORK " As guests go, in the megastar-driven dinner party that Broadway has become, Bradley Cooper makes for respectful, well disciplined company. That he's not the exhilarating life of that party may be a function of the limits of his technique, but more likely, of the various constraints he's under in the tepid  revival of "The Elephant Man" that had its official opening Sunday night at the Booth The…