fix: Don't generate new timestamp for re-sent messages (#7889)

Timestamp renewal was introduced in 1dbf924c6a "feat:
chat::resend_msgs: Guarantee strictly increasing time in the Date header" so that re-sent messages
can be deduplicated on the reciver side, but the deduplication logic doesn't depend on "Date"
anymore.

src/chat.rs

@@ -4664,7 +4664,6 @@ pub async fn resend_msgs(context: &Context, msg_ids: &[MsgId]) -> Result<()> {
             }
             msg_state => bail!("Unexpected message state {msg_state}"),
         }
-        msg.timestamp_sort = create_smeared_timestamp(context);
         if create_send_msg_jobs(context, &mut msg).await?.is_empty() {
             continue;
         }