vi: Refresh Vietnamese translation (#2061)

The English contents has changed, leading to untranslated session
outline and schedule because the msgid no longer match the original
contents. Additionally, incorrect file names are listed in the comment.
This PR follow the steps outlined in [Refreshing an Existing
Translation](https://github.com/google/comprehensive-rust/blob/main/TRANSLATIONS.md#refreshing-an-existing-translation)
to refresh the Vietnamese translation file. After the update, some
translated session outlines were no longer appropriated, so this PR also
updates all of them

Author: l0ngvh