Auto merge of #4542 - equal-l2:sha256-crypto-hash, r=alexcrichton

Use crypto-hash to calculate SHA256

`crypto-hash` is an abstraction library for native hash libraries.
It uses CryptoAPI on Windows, CommonCrypto on macOS, and OpenSSL on *nix.

This PR will also remove `openssl` and `advapi32-sys` from dependencies since they are only used for calculating SHA256, which is superseded by `crypto-hash`.
(`crypto-hash` itself uses `openssl` and `advapi32-sys` though)