reewide: Purge all uses stdenv.system and top-level system

It is deprecated and will be removed after 18.09.

pkgs/applications/editors/sublime/2/default.nix

@@ -6,7 +6,7 @@ in
 stdenv.mkDerivation rec {
   name = "sublimetext-2.0.2";
   src =
-    if stdenv.system == "i686-linux" then
+    if stdenv.hostPlatform.system == "i686-linux" then
       fetchurl {
         name = "sublimetext-2.0.2.tar.bz2";
         url = http://c758482.r82.cf2.rackcdn.com/Sublime%20Text%202.0.2.tar.bz2;

pkgs/applications/editors/sublime/3/common.nix

@@ -13,13 +13,13 @@ let
     ++ stdenv.lib.optional gksuSupport "/usr/bin/gksudo=${gksu}/bin/gksudo";
 in let
   archSha256 =
-    if stdenv.system == "i686-linux" then
+    if stdenv.hostPlatform.system == "i686-linux" then
       x32sha256
     else
       x64sha256;
 
   arch =
-    if stdenv.system == "i686-linux" then
+    if stdenv.hostPlatform.system == "i686-linux" then
       "x32"
     else
       "x64";