goPackages.git-lfs: remove man and script

After dc3ec30 these are back in $PATH where they don't belong. Just
remove them ‘for now’.

(`postInstall` seems to have been modified in the gap between 741bf84,
where those files were simply removed, and 6602f49.)

pkgs/top-level/go-packages.nix

@@ -776,6 +776,10 @@ let
         go generate ./commands
       popd
     '';
+
+    postInstall = ''
+      rm -v $bin/bin/{man,script}
+    '';
   };
 
   glide = buildFromGitHub {