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/organisations/test_organisations.py

@@ -1724,11 +1724,10 @@ def test_download_organisation_agreement(
     )
 
     client_request.login(platform_admin_user)
-    response = client_request.get(
+    response = client_request.get_response(
         'main.organisation_download_agreement',
         org_id=ORGANISATION_ID,
         _expected_status=expected_status,
-        _raw_response=True
     )
 
     if expected_file_served: