Avoid some StorePath -> Path -> StorePath roundtrips
Avoid some StorePath -> Path -> StorePath roundtrips

There were done when StorePath was defined in Rust and there were some
FFI issues. This is no longer an issue.

NixOS/nix,NixOS/nix,rycee/nix,NixOS/nix,rycee/nix,NixOS/nix,rycee/nix,rycee/nix,NixOS/nix,rycee/nix