index hash has changed

[ehuss]

As a result of #8522 changing the hash computation, the crates.io index path has changed from the long-running github.com-1ecc6299db9ec823 to github.com-f1e60147b9cdaa30. My main concern here is the increase in disk usage, since these tend to be kinda weighty (the new one is 81MB, my old one had accumulated 230MB).

I'm wondering if it would be better to try to match the old hash for this circumstance? Since Cargo doesn't have any sort of built-in garbage collection, the old index will persist unless the user manually deletes it.