Remove reference to unused hidden attribute of {msg}.
@@ -305,22 +305,6 @@ NOTE: In the example above, the `attendees` subkeys are accessed using null-safe
accesses (e.g. `$attendees[1]?.gender` instead of `$attendees[1].gender`) see
the [pitfalls section](#placholder_error) for more information about this.
-### Hidden
-
-If you need to hide your messages from volunteer translators outside of Google
-(if you're concerned that confidential information might be leaked about a new
-product/feature), you can set the `hidden` attribute on the message to ensure
-that your message is only translated by non-volunteers.
-
-```soy
-{msg desc="Description of the message" hidden="true"}
- Message for a super secret new feature.
-{/msg}
-```
-
-Once your product/feature has been released, you should remove the hidden
-attribute to restore access for all translators.
-
### Alternate IDs
If you migrate from another message management scheme to Soy, that will likely
