test: cleanup karma (jsunit) tests and move files_external to Cypress

[susnux]

Summary

• Remove unused legacy tests for legacy files list integration that does not exist anymore...
• Move files external tests from Karma ("jsunit") to Cypress
• Remove legacy stuff from karma config, its only used for core tests anymore (thats a todo for a follow up).

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)