Removed unnecessary app_template directory from flake8 exclude.

Unnecessary since abc0777b63057e2ff97eee2ff184356051e14c47 where the
extension was changed to not be ".py".

setup.cfg

@@ -56,7 +56,7 @@ doc_files = docs extras AUTHORS INSTALL LICENSE README.rst
 install-script = scripts/rpm-install.sh
 
 [flake8]
-exclude = build,.git,.tox,./django/conf/app_template/*,./tests/.env
+exclude = build,.git,.tox,./tests/.env
 ignore = W504,W601
 max-line-length = 119