imap: do not delete duplicates

Currently if user moves the message into some other folder and then
moves the message back, the message is considered duplicate even
though previous copy was already deleted. This is a common problem
reported by users at least twice.

Keeping duplicates does no harm except for additional storage usage.
If the message is later deleted by the user, all the copies on the
server will be deleted. anyway.

src/imap.rs

@@ -713,19 +713,6 @@ impl Imap {
                 None => folder.to_string(),
             };
 
-            let duplicate = context
-                .sql
-                .count(
-                    "SELECT COUNT(*)
-                     FROM imap
-                     WHERE rfc724_mid=?
-                     AND folder=?
-                     AND uid<?",
-                    paramsv![message_id, &target, uid],
-                )
-                .await?
-                > 0;
-
             context
                 .sql
                 .execute(
@@ -734,13 +721,7 @@ impl Imap {
                        ON CONFLICT(folder, uid, uidvalidity)
                        DO UPDATE SET rfc724_mid=excluded.rfc724_mid,
                                      target=excluded.target",
-                    paramsv![
-                        message_id,
-                        folder,
-                        uid,
-                        uid_validity,
-                        if duplicate { "" } else { &target }
-                    ],
+                    paramsv![message_id, folder, uid, uid_validity, &target],
                 )
                 .await?;