change wording of QueryCannotBePostedAsFact to QueryCannotBeDefinedAsFact, remove old commented code in read.rs

src/prolog/machine/toplevel.rs

@@ -1290,7 +1290,7 @@ impl<'a> TopLevelBatchWorker<'a> {
                 TopLevel::Declaration(decl) =>
                     return Ok(Some(decl)),
                 TopLevel::Query(_) =>
-                    return Err(SessionError::QueryCannotBePostedAsGoal),
+                    return Err(SessionError::QueryCannotBeDefinedAsFact),
             }
         }