insight-chat: drop the dead SmsApiClient::search_messages wrapper

The post-PR-4 delegation kept it as a convenience for callers that
don't filter by contact, but nothing actually uses it. Delete to clear
the dead_code warning. search_messages_with_contact remains as the
single entry point.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/ai/sms_client.rs

@@ -262,20 +262,8 @@ impl SmsApiClient {
     ///   - "semantic" embedding similarity
     ///   - "hybrid"   both merged via reciprocal rank fusion (recommended)
     ///
-    /// Equivalent to `search_messages_with_contact(query, mode, limit, None)`;
-    /// kept as a convenience for callers that don't filter by contact.
-    pub async fn search_messages(
-        &self,
-        query: &str,
-        mode: &str,
-        limit: usize,
-    ) -> Result<Vec<SmsSearchHit>> {
-        self.search_messages_with_contact(query, mode, limit, None).await
-    }
-
-    /// Same shape as `search_messages` but with optional `contact_id`. The
-    /// SMS-API endpoint accepts contact_id natively; date filtering is the
-    /// caller's responsibility (post-filter on the returned rows).
+    /// The SMS-API endpoint accepts `contact_id` natively; date filtering is
+    /// the caller's responsibility (post-filter on the returned rows).
     pub async fn search_messages_with_contact(
         &self,
         query: &str,