[auto-toolstate] Upload the toolstate result to an external git repository, and removes BuildExpectation
This PR consists of 3 commits.
1. (Steps 4–6) The `toolstate.json` output previously collected is now pushed to the https://github.com/rust-lang-nursery/rust-toolstate repository.
2. (Step 7) Revert commit ab018c7, thus removing all traces of `BuildExpectation` and `toolstate.toml`.
3. (Step 8) Adjust CONTRIBUTION.md for the new procedure.
These are the last steps of #45861. After this PR, the toolstate will be automatically computed and published to https://rust-lang-nursery.github.io/rust-toolstate/. There is no need to manage toolstate.toml again.
Closes#45861.
503153e950