Remove temporary raw_response argument

We added a new argument to `client_request.get` and
`client_request.post` to specify that it should return a raw `Response`
object rather than an instance of `BeautifulSoup`.

This is useful because sometimes we need to look at stuff like the
response headers.

However it turns out we already have a separate method for this, so
rather than invent something new I think it’s better to stick with the
thing we already have.

tests/app/main/views/uploads/test_upload_contact_list.py

@@ -660,11 +660,10 @@ def test_download_contact_list(
         'app.models.contact_list.s3download',
         return_value='phone number\n07900900321'
     )
-    response = client_request.get(
+    response = client_request.get_response(
         'main.download_contact_list',
         service_id=SERVICE_ONE_ID,
         contact_list_id=fake_uuid,
-        _raw_response=True,
     )
     assert response.headers['Content-Type'] == (
         'text/csv; '