Move challenge http status code logic

See: 3ea67df373/registry/handlers/app.go (L498)

Per the comment on line 498, this moves the logic of setting the http
status code into the serveJSON func, leaving the auth.Challenge.ServeHTTP()
func to just set the auth challenge header.

Signed-off-by: Doug Davis <dug@us.ibm.com>

registry/auth/token/accesscontroller.go

@@ -117,10 +117,9 @@ func (ac *authChallenge) SetHeader(header http.Header) {
 }
 
 // ServeHttp handles writing the challenge response
-// by setting the challenge header and status code.
+// by setting the challenge header.
 func (ac *authChallenge) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	ac.SetHeader(w.Header())
-	w.WriteHeader(ac.Status())
 }
 
 // accessController implements the auth.AccessController interface.