fetchurl: Remove some compatibility hacks

pkgs/build-support/fetchurl/default.nix

@@ -1,4 +1,4 @@
-{stdenv, curl}: # Note that `curl' may be `null', in case of the native stdenv.
+{ stdenv, curl }: # Note that `curl' may be `null', in case of the native stdenv.
 
 let
 
@@ -17,10 +17,7 @@ let
 
   # Names of the master sites that are mirrored (i.e., "sourceforge",
   # "gnu", etc.).
-  sites =
-    if builtins ? attrNames
-    then builtins.attrNames mirrors
-    else [] /* backwards compatibility */;
+  sites = builtins.attrNames mirrors;
 
   impureEnvVars = [
     # We borrow these environment variables from the caller to allow
@@ -38,7 +35,7 @@ let
   ] ++ (map (site: "NIX_MIRRORS_${site}") sites);
 
 in
-      
+
 { # URL to fetch.
   url ? ""
 
@@ -79,9 +76,9 @@ stdenv.mkDerivation {
     if showURLs then "urls"
     else if name != "" then name
     else baseNameOf (toString (builtins.head urls_));
-    
+
   builder = ./builder.sh;
-  
+
   buildInputs = [curl];
 
   urls = urls_;
@@ -90,9 +87,6 @@ stdenv.mkDerivation {
   # (http://nixos.org/tarballs) over the original URLs.
   preferHashedMirrors = true;
 
-  # Compatibility with Nix <= 0.7.
-  id = md5;
-
   # New-style output content requirements.
   outputHashAlgo = if outputHashAlgo != "" then outputHashAlgo else
       if sha256 != "" then "sha256" else if sha1 != "" then "sha1" else "md5";