Remove strings that are not used anymore

[TimoPtr]

Summary

We had some strings not used anymore in the project, mostly because I've removed the onboarding but also some others.

Checklist

• New or updated tests have been added to cover the changes following the testing guidelines.
• The code follows the project's code style and best_practices.
• The changes have been thoroughly tested, and edge cases have been considered.
• Changes are backward compatible whenever feasible. Any breaking changes are documented in the changelog for users and/or in the code for developers depending on the relevance.

[jpelgrom]

It builds and there were no stand outs for me, so I'm assuming it's OK - I didn't search for every string manually.

As previously mentioned some of these changes do not need the use_new_onboarding branch, please be mindful of that in the future (getting very big).