Mobile App: Remove component loading support (#23025)

Loading a component defined in a registration didn't actually work and was undocumented, so let's just remove it instead of fixing #23005.

## Checklist:
  - [X] The code change is tested and works locally.
  - [X] Local tests pass with `tox`. **Your PR cannot be merged unless tests pass**
  - [X] There is no commented out code in this PR.

tests/components/mobile_app/test_http_api.py

@@ -80,28 +80,3 @@ async def test_registration(hass, hass_client):  # noqa: F811
     decrypted_data = decrypted_data.decode("utf-8")
 
     assert json.loads(decrypted_data) == {'one': 'Hello world'}
-
-
-async def test_register_invalid_component(authed_api_client):  # noqa: F811
-    """Test that registration with invalid component fails."""
-    resp = await authed_api_client.post(
-        '/api/mobile_app/registrations', json={
-            'app_component': 'will_never_be_valid',
-            'app_data': {'foo': 'bar'},
-            'app_id': 'io.homeassistant.mobile_app_test',
-            'app_name': 'Mobile App Tests',
-            'app_version': '1.0.0',
-            'device_name': 'Test 1',
-            'manufacturer': 'mobile_app',
-            'model': 'Test',
-            'os_name': 'Linux',
-            'os_version': '1.0',
-            'supports_encryption': True
-        }
-    )
-
-    assert resp.status == 400
-    register_json = await resp.json()
-    assert 'error' in register_json
-    assert register_json['success'] is False
-    assert register_json['error']['code'] == 'invalid_component'