Remove the hg up null workaround as it is no longer needed

[marco-c]

The new workaround from https://bugzilla.mozilla.org/show_bug.cgi?id=1720302 is much faster than hg up null we introduced in #68.

The workaround script lives at https://gist.github.com/zzzeid/46f7d8cc794f9fccf999bb8356f981be.

[abpostelnicu]

@marco-c if the current solution works, why don't we wait for the final patch?

[marco-c]

Yeah, maybe better to wait at this point. We can decide to use this new workaround in case we see the bot being too slow because of hg up null.

[marco-c]

The repo was fixed, so we can actually remove the workaround.