Remove all sentences in sentence collector for Ukrainian

First of all, you can find the approved and exported sentences here: https://github.com/mozilla/voice-web/blob/master/server/data/uk/sentence-collector.txt

Approximately how many sentences are we talking about? And can you give me your username?

For my future reference: the deletion query would need to delete all not-approved sentences, but not those that Artem has already approved!