llvmPackages_10: removed extra polly-build

There is no good reason to have separate builds for polly and no-polly
versions. wwwwwThe reason for the two versions was (as far as I can
tell) to defer rebuilds (see ed60483257).
Polly is now enabled by default.

pkgs/development/compilers/llvm/10/default.nix

@@ -30,16 +30,11 @@ let
   in {
 
     llvm = callPackage ./llvm.nix { };
-    llvm-polly = callPackage ./llvm.nix { enablePolly = true; };
 
     clang-unwrapped = callPackage ./clang {
       inherit (tools) lld;
       inherit clang-tools-extra_src;
     };
-    clang-polly-unwrapped = callPackage ./clang {
-      inherit clang-tools-extra_src;
-      llvm = tools.llvm-polly;
-    };
 
     llvm-manpages = lowPrio (tools.llvm.override {
       enableManpages = true;