feat!: stop tracking contact verification

Since V2 a contact is its key, there is no address-to-key binding left to verify.

The JSONRPC and FFI APIs are unchanged and report nothing as verified.

BREAKING CHANGE: the statistics JSON sent to the self-reporting-bot on Android changes: Contacts have `encrypted` instead of `verified` and lose `transitive_chain` properties and message stats have `encrypted` instead of `verified` and `unverified_encrypted`, and securejoin invites lose `already_verified`. The collecting bot stores incoming reports verbatim but analysis will have to make sense of older and newer reports.

src/chat.rs

@@ -2683,7 +2683,7 @@ async fn prepare_send_msg(
 
     let skip_fn = |reason: &CantSendReason| match reason {
         CantSendReason::ContactRequest => {
-            // Allow securejoin messages, they are supposed to repair the verification.
+            // Allow securejoin messages.
             // If the chat is a contact request, let the user accept it later.
             msg.param.get_cmd() == SystemMessage::SecurejoinMessage
         }