Remove no longer applicable section on Flask migration docs

No longer needed after #3782

doc/extensions/flask-migration.rst

@@ -45,87 +45,3 @@ misconfigured.
     package that provides wrappers for cross-version CKAN compatibility::
 
         from ckantoolkit import config
-
-
-------------------------------------------------------------------------------
-Wrap ``url_for`` calls in tests with a test request context (``RuntimeError``)
-------------------------------------------------------------------------------
-
-Starting from CKAN 2.8 you might get the following exception when running the
-tests::
-
-    RuntimeError: Attempted to generate a URL without the application context being
-    pushed. This has to be executed when application context is available.
-
-Users familiar with Flask may recognize this exception. Basically the Flask
-router (called internally by ``ckan.lib.helpers.url_for``) requires you to be
-in the context on a web request when calling it (You can learn more about this
-in the `Flask documentation <http://flask.pocoo.org/docs/testing/>`_). What this
-means is that a test like this will raise the above exception::
-
-    from ckan.plugins.toolkit import url_for    
-    from ckan.tests.helpers import FunctionalTestBase
-
-    class TestSearch(FunctionalTestBase):
-
-        def test_search_page_works(self):
-
-            app = self._get_test_app()
-            url = url_for(controller='package', action='search')              
-            res = app.get(url)
-
-To fix it, we need to wrap the ``url_for`` call with a test request context::
-
-    from ckan.plugins.toolkit import url_for    
-    from ckan.tests.helpers import FunctionalTestBase
-
-    class TestSearch(FunctionalTestBase):
-
-        def test_search_page_works(self):
-
-            app = self._get_test_app()
-            with app.flask_app.test_request_context():
-                url = url_for(controller='package', action='search')              
-            res = app.get(url)
-
-If you are not extending ``FunctionalTestBase`` you can get an instance of the
-test app client in order to create the test request context::
-
-    from ckan.plugins.toolkit import url_for
-    from ckan.tests.helpers import _get_test_app
-
-    class TestSearch(object):
-        def test_search_page_works(self):
-
-            app = _get_test_app()
-            with app.flask_app.test_request_context():
-                url = url_for(controller='package', action='search')              
-            res = app.get(url)
-
-Note that the call to ``url_for`` might not be explicitly done in the test
-itself but rather internally. For instance consider the following example::
-
-
-    from ckan.tests.helpers import FunctionalTestBase
-
-    class TestDatastore(FunctionalTestBase):
-
-        def test_create_datastore_only_view(self):
-            # ...
-            # datastore_create will call ``url_for`` internally (or trigger
-            # something that calls it) so we need a Flask test context
-            with self.app.flask_app.test_request_context():
-                result = helpers.call_action('datastore_create', **data)
-
-Or this one::
-
-    import ckan.lib.dictization.model_dictize as model_dictize
-    from ckan.tests.helpers import _get_test_app
-
-    class TestDictize(object):
-
-        def test_resource_dictize(self):
-            # Internally resource_dictize calls ``url_for`` so we need a test context
-            app = helpers._get_test_app()
-            with app.flask_app.test_request_context():
-                resource_dict = model_dictize.resource_dictize(...)