"Unsafe Browser can be used in all languages supported in Tails" test suite scenario assumes PO files are present when it's not guaranteed

Original title: "Missing localization for ko and pl in 4.19~rc1"

In commit 6808f505 the po/ko.po and po/pl.po locales were dropped for some reason. The lack of Korean support makes the The Unsafe Browser can be used in all languages supported in Tails scenario fail with:

Then the Unsafe Browser works in all supported languages                       # features/step_definitions/unsafe_browser.rb:33                                                     
  Could not find a locale for 'ko:KR' (RuntimeError)

(And probably it would also fail later for pl:PL.