Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
       ServerFailure(_) => Status::InternalServerError,
       NoClient | NoPlayer(_) | GameBeingDestroyed(_)
         => Status::NotFound,
-      OE::PieceHeld | OE::PieceImmoveable |
+      OE::PieceHeld |
       BadJSON(_)
         => Status::BadRequest,
     }
 
   BadJSON(serde_json::Error),
   #[error("referenced piece is gone (maybe race)")]
   PieceHeld, // xxx should be _inapplicable_
-  #[error("improper UI operation")]
-  PieceImmoveable, // xxx should be _inapplicable_
 }
 
 #[derive(Error,Debug)]