nightly Cargo fails on missing README.md, breaks remove_dir_all crate and all transitive callers

[oconnor663]

Here's the downstream issue: XAMPPRocky/remove_dir_all#19

This issue began very recently. It repros on 1.46.0-nightly (a37c32e2d 2020-06-11), but it did not repro on rustc 1.46.0-nightly (feb3536eb 2020-06-09). Missing components in that latest build mean that I think only people running rustup set profile minimal are seeing the break currently, but it will spread with the next complete nightly build.

In this case, it think the remove_dir_all crate will be able to publish a new patch version that includes a fix. However, this won't help binary callers that have committed a Cargo.lock file. This Cargo behavior change might be a stability hazard.

[jonas-schievink]

Duplicate of #73279

[oconnor663]

Woops, thank you.