Rename two hash constructors to proper functions

src/libexpr/primops/fetchGit.cc

src/libexpr/primops/fetchMercurial.cc

src/libfetchers/git.cc

src/libfetchers/github.cc

src/libfetchers/mercurial.cc

src/libfetchers/path.cc

src/libstore/content-address.cc

src/libstore/daemon.cc

src/libstore/derivations.cc

src/libstore/legacy-ssh-store.cc

src/libstore/local-store.cc

src/libstore/nar-info-disk-cache.cc

src/libstore/nar-info.cc

src/libstore/remote-store.cc

src/libstore/store-api.cc

src/libutil/hash.cc

src/libutil/hash.hh

src/nix-prefetch-url/nix-prefetch-url.cc

src/nix-store/nix-store.cc

src/nix/hash.cc