docs: do not talk about verified chats in securejoin QR-scanning functions

The chat is always going to be encrypted, this is enough.
We actually do mark the contact as verified,
but the meaning of this verification is unclear
and we don't even display it visibly in the chat anymore.

deltachat-jsonrpc/src/api.rs

@@ -935,7 +935,6 @@ impl CommandApi {
     ///     to `check_qr()`.
     ///
     /// **returns**: The chat ID of the joined chat, the UI may redirect to the this chat.
-    ///         A returned chat ID does not guarantee that the chat is protected or the belonging contact is verified.
     ///
     async fn secure_join(&self, account_id: u32, qr: String) -> Result<u32> {
         let ctx = self.get_context(account_id).await?;