chore(deps): bump express and ln-service in /backup-server

Removes [express](https://github.com/expressjs/express). It's no longer used after updating ancestor dependency [ln-service](https://github.com/alexbosworth/ln-service). These dependencies need to be updated together.


Removes `express`

Updates `ln-service` from 56.13.0 to 57.27.1
- [Changelog](https://github.com/alexbosworth/ln-service/blob/master/CHANGELOG.md)
- [Commits](https://github.com/alexbosworth/ln-service/commits)

---
updated-dependencies:
- dependency-name: express
  dependency-version: 
  dependency-type: indirect
- dependency-name: ln-service
  dependency-version: 57.27.1
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]