fix: move Taiwanese translations to correct file (#1864)

This (hopefully) fixes #1857.

In our other Flutter applications, where this works correctly, the
`zh_Hant` language code for traditional Chinese (weblate) is mapped to
`zh_TW` arb files (repository). For the app-center it seems like a
`zh_Hant` arb file was created by weblate, which isn't supported by our
current localization setup. So deleting the empty `zh_TW` file and
renaming the existing file with the Taiwanese translations `zh_Hant` ->
`zh_TW` should fix the issue.

UDENG-5307