corepkgs/fetchurl: Call the shell directly instead of using the shebang

corepkgs/fetchurl.nix

@@ -10,7 +10,8 @@ assert (outputHash != "" && outputHashAlgo != "")
 
 derivation {
   name = baseNameOf (toString url);
-  builder = ./fetchurl.sh;
+  builder = shell;
+  args = [ "-e" ./fetchurl.sh ];
 
   # Compatibility with Nix <= 0.7.
   id = md5;

corepkgs/fetchurl.sh

@@ -1,5 +1,3 @@
-#! @shell@ -e
-
 echo "downloading $url into $out"
 
 $curl --fail --location --max-redirs 20 "$url" > "$out"