The GPT backend is cool, but it's also very slow, prone to request
errors and quite expensive.
This switches to Yandex Translate instead which for all posts that I
tested seems to be totally fine.
Change-Id: I5217113995b701508a83e7782eb1325957996719
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8826
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>