Parse QR codes without using Param

Param should only be used to parse dictionaries stored in SQL database, not external data.

Since Param parser has been extended to escape newlines with newlines, QR-codes parser started to treat && as escaped &, which is wrong.

This change also uses String keys like "n" for "name" instead of completely unrelated constants like Param::SetLongitude.

src/param.rs

@@ -127,15 +127,6 @@ pub enum Param {
     /// For Chats
     Devicetalk = b'D',
 
-    /// For QR
-    Auth = b's',
-
-    /// For QR
-    GroupId = b'x',
-
-    /// For QR
-    GroupName = b'g',
-
     /// For MDN-sending job
     MsgId = b'I',
 }
@@ -431,14 +422,6 @@ mod tests {
         assert_eq!(params.to_string().parse::<Params>().unwrap(), params);
     }
 
-    #[test]
-    fn test_regression() {
-        let p1: Params = "a=cli%40deltachat.de\nn=\ni=TbnwJ6lSvD5\ns=0ejvbdFSQxB"
-            .parse()
-            .unwrap();
-        assert_eq!(p1.get(Param::Forwarded).unwrap(), "cli%40deltachat.de");
-    }
-
     #[async_std::test]
     async fn test_params_file_fs_path() {
         let t = TestContext::new().await;