Auto merge of #7324 - Eh2406:two-copys-of-hash, r=alexcrichton
Auto merge of #7324 - Eh2406:two-copys-of-hash, r=alexcrichton

don't need to copy this string

This removes a `String::clone` that I noticed when profiling no-op builds of cargo, benchmarks show a barely visible improvement. Looks like it was added in #6880, but I am not sure why.

tsurai/cargo,tsurai/cargo,eminence/cargo,tshepang/cargo,tsurai/cargo,vojtechkral/cargo,tsurai/cargo,rustyhorde/cargo,rustyhorde/cargo,rustyhorde/cargo,tshepang/cargo,tshepang/cargo,tshepang/cargo,nipunn1313/cargo,vojtechkral/cargo,rust-lang/cargo,rust-lang/cargo,nipunn1313/cargo,eminence/cargo,tsurai/cargo,rust-lang/cargo,rust-lang/cargo,vojtechkral/cargo,rustyhorde/cargo,vojtechkral/cargo,nipunn1313/cargo,nipunn1313/cargo,eminence/cargo,eminence/cargo