dc_receive_imf: remove Received: based draft detection heuristic

Proper draft detection was implemented in
bf7f64d50b

Removing this heuristic also removes the need to pass IMAP folder name
around.

src/chatlist.rs

@@ -503,7 +503,6 @@ mod tests {
                  Date: Sun, 22 Mar 2021 22:37:57 +0000\n\
                  \n\
                  hello foo\n",
-            "INBOX",
             false,
         )
         .await?;
@@ -564,7 +563,6 @@ mod tests {
                  Date: Sun, 22 Mar 2021 22:38:57 +0000\n\
                  \n\
                  hello foo\n",
-            "INBOX",
             false,
         )
         .await?;