echo: Fix handling of `locally_echoed` flag after successful msg resend.

The `on_success` function within `echo.resend_message` is executed when
the server successfully acknowledges a resent message. In this scenario,
the `locally_echoed` flag should be set to false, as the message has
been confirmed by the server.

This behavior is already correctly handled within the
`echo.reify_message_id()` function, which is triggered through the
`compose.send_message_success()` flow.

However, the on_success function incorrectly sets the `locally_echoed`
flag to true, which is unnecessary and likely a mistake. This led to
the bug where message controls would disappear from the resent messages
on slow networks.

This commit removes the erroneous line to ensure proper flag handling
during message resend.

web/src/echo.ts

@@ -171,7 +171,6 @@ function resend_message(
     function on_success(raw_data: unknown): void {
         const data = send_message_api_response_schema.parse(raw_data);
         const message_id = data.id;
-        message.locally_echoed = true;
 
         hide_retry_spinner($row);