Prune stale translation keys

[billybonks]

As features are added and removed some translation keys will be become stale, and should be pruned from json file

[tangollama]

@billybonks agreed. do you have specific processes that you want to be sure people follow for translations, or is this something that could be put into a linter? That seems to me to be ideal. Thoughts?

[tangollama]

If the action here would be to add a linter to the system that validated that all translation keys were referenced (if that's possible), then we can do something with this. If not, we need to document this as part of the contribution guide.

[mqchau]

Helped by #1037

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.