Revert "hello: 2.10 -> 2.12" (#158328)

This reverts commit 3e4412db9c3503b94aab80c9c4d7dbf50e096857.

broke `stdenvBootstrapTools.x86_64-darwin.test`, blocking nixpkgs-unstable

pkgs/applications/misc/hello/default.nix

···
 
 stdenv.mkDerivation rec {
   pname = "hello";
-  version = "2.12";
+  version = "2.10";
 
   src = fetchurl {
     url = "mirror://gnu/hello/${pname}-${version}.tar.gz";
-    sha256 = "1ayhp9v4m4rdhjmnl2bq3cibrbqqkgjbl3s7yk2nhlh8vj3ay16g";
+    sha256 = "0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i";
   };
 
   doCheck = true;