nix-prefetch-url: Run in constant memory when using RemoteStore
nix-prefetch-url: Run in constant memory when using RemoteStore

Fixes #3684.

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