settings: Remove useless commented mypy type.

Legacy settings contained type "Dict" which were removed in zulip 9.0,
so this type was wrong, but it also serves no purpose.

(The non-commented types are checked in the development environment).

zproject/prod_settings_template.py

@@ -572,7 +572,7 @@ SOCIAL_AUTH_SAML_SUPPORT_CONTACT = {
 ## algorithm must be configured here.
 ##
 ## See https://zulip.readthedocs.io/en/latest/production/authentication-methods.html#jwt
-# JWT_AUTH_KEYS: Dict[str, Any] = {
+# JWT_AUTH_KEYS = {
 #     # Subdomain for which this JWT configuration will apply.
 #     "zulip": {
 #         # Shared secret key used to validate jwt tokens, which should be stored