fix: repair malformed policy_schema.json (extra closing braces)

Fixes 4 pre-existing TestJsonSchema test failures caused by orphaned
closing braces at lines 40-42 from a bad merge.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: imran-siddique

packages/agent-os/src/agent_os/policies/policy_schema.json

@@ -36,9 +36,6 @@
       "$ref": "#/definitions/A2AConversationPolicy",
       "description": "Policy for A2A conversation monitoring and feedback loop prevention."
     }
-  },
-      "additionalProperties": false
-    }
   },
   "additionalProperties": false,
   "definitions": {