fix build with newer yesod

Assistant/WebApp/Configurators/Edit.hs

@@ -151,7 +151,7 @@ editRepositoryAForm def = RepoConfig
 	help = [whamlet|<a href="@{RepoGroupR}">What's this?</a>|]
 
 	associateddirectory = case repoAssociatedDirectory def of
-		Nothing -> aopt dummyField "" Nothing
+		Nothing -> aopt hiddenField "" Nothing
 		Just d -> aopt textField "Associated directory" (Just $ Just d)
 
 getEditRepositoryR :: UUID -> Handler RepHtml

Assistant/WebApp/Form.hs

@@ -39,13 +39,6 @@ passwordField = F.passwordField
 |]
 	}
 
-{- Useful in an AForm when sometimes a field is not used. -}
-dummyField :: RenderMessage master FormMessage => Field sub master Text
-dummyField = Field
-	{ fieldView = \_theId _name _attrs _val _isReq -> return ()
-	, fieldParse = const $ return $ Right Nothing
-	}
-
 {- Makes a note widget be displayed after a field. -}
 withNote :: Field sub master v -> GWidget sub master () -> Field sub master v
 withNote field note = field { fieldView = newview }