fix(relay): drop now-unused IntoResponse import

Follow-up to dc2df1667: moving the response conversion out to the call
sites left `IntoResponse` unused in the admin module.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Signed-off-by: Eli Foster <efoster@squareup.com>

crates/buzz-relay/src/api/admin/mod.rs

@@ -10,7 +10,7 @@ use axum::{
     extract::{Path, Query, State},
     http::{header, HeaderMap, HeaderValue},
     middleware::{self, Next},
-    response::{IntoResponse, Response},
+    response::Response,
     routing::get,
     Json, Router,
 };