codex: strip guardian reviewThreadId from app protocol

Keep the guardian rollout attachment plumbing for /feedback uploads, but remove the unnecessary app-server notification/schema field so the PR stays narrowly scoped.

Co-authored-by: Codex <noreply@openai.com>

codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json

@@ -4554,12 +4554,6 @@
             "null"
           ]
         },
-        "reviewThreadId": {
-          "type": [
-            "string",
-            "null"
-          ]
-        },
         "riskLevel": {
           "anyOf": [
             {