Revert "Revert "pythonPackages.django: clarify versions, remove django_lts attribute""

Every major version will have only a single LTS release, which is the
one we typically keep in Nixpkgs.

https://www.djangoproject.com/download/

This reverts commit af8a48c3c1.

pkgs/development/python-modules/django-oauth-toolkit/default.nix

@@ -1,5 +1,5 @@
 { stdenv, buildPythonPackage, fetchFromGitHub
-, django_2_2, requests, oauthlib
+, django, requests, oauthlib
 }:
 
 buildPythonPackage rec {
@@ -13,7 +13,7 @@ buildPythonPackage rec {
     sha256 = "1zbksxrcxlqnapmlvx4rgvpqc4plgnq0xnf45cjwzwi1626zs8g6";
   };
 
-  propagatedBuildInputs = [ django_2_2 requests oauthlib ];
+  propagatedBuildInputs = [ django requests oauthlib ];
 
   # django.core.exceptions.ImproperlyConfigured: Requested setting OAUTH2_PROVIDER, but settings are not configured. You must either define the environment variable DJANGO_SETTINGS_MODULE or call settings.configure() before accessing settings
   doCheck = false;