refactor: Remove unused OBJECTQL_PLUGIN_MARKER symbol

Co-authored-by: hotlong <50353452+hotlong@users.noreply.github.com>

Author: Copilot

packages/runtime/src/objectql-plugin.ts

@@ -1,11 +1,6 @@
 import { ObjectQL } from '@objectstack/objectql';
 import { RuntimePlugin, RuntimeContext } from '@objectstack/types';
 
-/**
- * Symbol to identify ObjectQL plugins
- */
-export const OBJECTQL_PLUGIN_MARKER = Symbol('objectql-plugin');
-
 /**
  * ObjectQL Engine Plugin
  * 
@@ -21,9 +16,6 @@ export class ObjectQLPlugin implements RuntimePlugin {
   name = 'com.objectstack.engine.objectql';
   type = 'objectql' as const;
 
-  // Mark this as an ObjectQL plugin for reliable detection
-  readonly [OBJECTQL_PLUGIN_MARKER] = true;
-  
   private ql: ObjectQL;
 
   /**