Bump express and web-ext

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


Removes `express`

Updates `web-ext` from 6.8.0 to 7.4.0
- [Release notes](https://github.com/mozilla/web-ext/releases)
- [Commits](mozilla/web-ext@6.8.0...7.4.0)

---
updated-dependencies:
- dependency-name: express
  dependency-type: indirect
- dependency-name: web-ext
  dependency-type: direct:development
...

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