Remove common.json localization file

[arcanistzed]

https://github.com/HacktheHill/track-the-hack/blob/main/public/locales/en/common.json
https://github.com/HacktheHill/track-the-hack/blob/main/public/locales/fr/common.json

### Tasks
- [x] Remove unused `unknown-error` localization key
- [x] Extract `contact-us`, `unknown-error`, `not-authorized-to-view-this-page` into an `Error.json` localization file
- [x] Extract `loading` into it's own localization file
- [x] Extract `description` into `Head.json`
- [x] Extract `hack-the-hill-logo-alt` into `FormPage.json`
- [ ] Remove all mentions of `"common"` in the `getStaticProps` function
- [ ] Once everything has been moved, delete the file

Don't forget to apply this to both languages.