chore: remove standalone relay (#3893)

Author: EmandM

com.unity.netcode.gameobjects/Editor/NetworkManagerRelayIntegration.cs

@@ -39,16 +39,11 @@
             "expression": "",
             "define": "COM_UNITY_MODULES_PHYSICS2D"
         },
-        {
-            "name": "com.unity.services.relay",
-            "expression": "1.0",
-            "define": "RELAY_SDK_INSTALLED"
-        },
         {
             "name": "com.unity.services.multiplayer",
             "expression": "0.2.0",
             "define": "MULTIPLAYER_SERVICES_SDK_INSTALLED"
         }
     ],
     "noEngineReferences": false
-}
+}