In this diff, we are removing the database item internal check for the device's notification token filed.
When the session item database method was introduced we are not discussed that in case the device has an expired or invalid notification token we should request the new one from it and make the current field empty, as well as the keyserver, does.
We are fixing the bug where the database error occurs in the case when the device token in the database became empty and the server will return a database error when retrieving the token in the next client connection.
The field can be empty and the database check shouldn't fail on this.
Linear task: [[ https://linear.app/comm/issue/ENG-2060/implement-tunnelbroker-grpc-messagesstream-api-handler-in-rust | ENG-2060 ]]