Drop asynctest (#44746)

tests/util/test_init.py

@@ -1,13 +1,12 @@
 """Test Home Assistant util methods."""
 from datetime import datetime, timedelta
+from unittest.mock import MagicMock, patch
 
 import pytest
 
 from homeassistant import util
 import homeassistant.util.dt as dt_util
 
-from tests.async_mock import MagicMock, patch
-
 
 def test_sanitize_filename():
     """Test sanitize_filename."""