fix: failures main tests since VAD agent initialization was changed

The test still expects the VAD agent to be started in main, rather than in the RI Communication Agent.

ref: N25B-356

test/unit/test_main.py

@@ -53,8 +53,6 @@ async def test_lifespan_agent_start_exception():
     Ensures exceptions are logged properly and re-raised.
     """
     with (
-        patch("control_backend.main.VADAgent.start", new_callable=AsyncMock),
-        patch("control_backend.main.VADAgent.reset_stream", new_callable=AsyncMock),
         patch(
             "control_backend.main.RICommunicationAgent.start", new_callable=AsyncMock
         ) as ri_start,