Inherit don’t duplicate API client constructor

This removes some code which is duplicative and obscure (ie it’s not
very clear why we do `"a" * 73` even though there is a Very Good Reason
for doing so).

app/notify_client/template_folder_api_client.py

@@ -2,10 +2,6 @@ from app.notify_client import NotifyAdminAPIClient, cache
 
 
 class TemplateFolderAPIClient(NotifyAdminAPIClient):
-    # Fudge assert in the super __init__ so
-    # we can set those variables later.
-    def __init__(self):
-        super().__init__('a' * 73, 'b')
 
     @cache.delete('service-{service_id}-template-folders')
     def create_template_folder(