Custom component loading cleanup (#14211)

* Clean up custom component loading

* Fix some tests

* Fix some stuff

* Make imports work again

* Fix tests

* Remove debug print

* Lint

tests/common.py

@@ -10,8 +10,7 @@ import logging
 import threading
 from contextlib import contextmanager
 
-from homeassistant import (
-    auth, core as ha, loader, data_entry_flow, config_entries)
+from homeassistant import auth, core as ha, data_entry_flow, config_entries
 from homeassistant.setup import setup_component, async_setup_component
 from homeassistant.config import async_process_component_config
 from homeassistant.helpers import (
@@ -138,9 +137,6 @@ def async_test_home_assistant(loop):
     hass.config.units = METRIC_SYSTEM
     hass.config.skip_pip = True
 
-    if 'custom_components.test' not in loader.AVAILABLE_COMPONENTS:
-        yield from loop.run_in_executor(None, loader.prepare, hass)
-
     hass.state = ha.CoreState.running
 
     # Mock async_start