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/context.rs

@@ -1043,7 +1043,7 @@ impl Context {
             self.get_config_int(Config::GossipPeriod).await?.to_string(),
         );
         res.insert(
-            "verified_one_on_one_chats",
+            "verified_one_on_one_chats", // deprecated 2025-07
             self.get_config_bool(Config::VerifiedOneOnOneChats)
                 .await?
                 .to_string(),