fetchgit: Remove incomplete/unneeded isURI check.
fetchgit: Remove incomplete/unneeded isURI check.

This check spuriously fails for e.g. git@github.com:NixOS/nixpkgs.git,
and even for ssh://git@github.com/NixOS/nixpkgs.git, and is made
redundant by the checks git itself will do when fetching the repo. We
instead pass a -- before passing the URI to git to avoid injection.

shlevy/nix,dezgeg/nix,rycee/nix,pikajude/nix,NixOS/nix,zimbatm/nix,vcunat/nix,ehmry/nix,vcunat/nix,dtzWill/nix,layus/nix,dtzWill/nix,peti/nix,vcunat/nix,ehmry/nix,zimbatm/nix,rycee/nix,dtzWill/nix,rycee/nix,ehmry/nix,peti/nix,NixOS/nix,NixOS/nix,peti/nix,dtzWill/nix,zimbatm/nix,ehmry/nix,shlevy/nix,zimbatm/nix,NixOS/nix,vcunat/nix,layus/nix,dezgeg/nix,layus/nix,rycee/nix,NixOS/nix,layus/nix,pikajude/nix,layus/nix,dezgeg/nix,rycee/nix,peti/nix,shlevy/nix,shlevy/nix,dezgeg/nix,dtzWill/nix,ehmry/nix,dezgeg/nix,pikajude/nix,ehmry/nix,shlevy/nix,peti/nix