fix: Remove extra FIXME comment

Author: KShivendu

supertokens_python/recipe/session/recipe_implementation.py

@@ -236,7 +236,6 @@ async def get_session(
             self,
             self.config,
             access_token_str,
-            # FIXME: expiry time cannot be None
             build_front_token(response.session.userId, expiry_time, payload),
             None,  # refresh_token
             anti_csrf_token,