Auto merge of #6171 - ehuss:metabuild-hash, r=alexcrichton
Auto merge of #6171 - ehuss:metabuild-hash, r=alexcrichton

Minor cleanup for metabuild hash

At the time I wrote this I was unaware of the util function that did the same
thing.

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