docs: deprecate protection-broken and related stuff (#7018)

came over these parts while targeting the new info message of
https://github.com/chatmail/core/pull/7008 in
https://github.com/deltachat/deltachat-ios/pull/2778 and
https://github.com/deltachat/deltachat-android/pull/3822

---------

Co-authored-by: Hocuri <hocuri@gmx.de>

src/imex.rs

@@ -804,7 +804,7 @@ async fn export_database(
                 "UPDATE backup.config SET value='0' WHERE keyname='verified_one_on_one_chats';",
                 [],
             )
-            .ok(); // If verified_one_on_one_chats was not set, this errors, which we ignore
+            .ok(); // Deprecated 2025-07. If verified_one_on_one_chats was not set, this errors, which we ignore
             conn.execute("DETACH DATABASE backup", [])
                 .context("failed to detach backup database")?;
             res?;