Drop asynctest (#44746)

tests/components/panel_custom/test_init.py

@@ -1,9 +1,9 @@
 """The tests for the panel_custom component."""
+from unittest.mock import Mock, patch
+
 from homeassistant import setup
 from homeassistant.components import frontend
 
-from tests.async_mock import Mock, patch
-
 
 async def test_webcomponent_custom_path_not_found(hass):
     """Test if a web component is found in config panels dir."""