Remove default_app_config for test apps and wagtail.core

wagtail/core/__init__.py

@@ -1 +0,0 @@
-default_app_config = "wagtail.core.apps.WagtailCoreAppConfig"

wagtail/test/demosite/__init__.py

@@ -1 +0,0 @@
-default_app_config = "wagtail.test.demosite.apps.DemositeAppConfig"

wagtail/test/i18n/__init__.py

@@ -1 +0,0 @@
-default_app_config = "wagtail.test.i18n.apps.I18nAppConfig"

wagtail/test/modeladmintest/__init__.py

@@ -1 +0,0 @@
-default_app_config = "wagtail.test.modeladmintest.apps.WagtailTestsAppConfig"

wagtail/test/routablepage/__init__.py

@@ -1 +0,0 @@
-default_app_config = "wagtail.test.routablepage.apps.WagtailRoutablePageTestsAppConfig"

wagtail/test/search/__init__.py

@@ -1 +0,0 @@
-default_app_config = "wagtail.test.search.apps.WagtailSearchTestsAppConfig"

wagtail/test/snippets/__init__.py

@@ -1 +0,0 @@
-default_app_config = "wagtail.test.snippets.apps.WagtailSnippetsTestsAppConfig"

wagtail/test/testapp/__init__.py

@@ -1 +0,0 @@
-default_app_config = "wagtail.test.testapp.apps.WagtailTestsAppConfig"