dockerTools.buildImage: do not add /nix/store in the tar stream

Since the /nix/store directory is not immutable, tar can fails if it
has to push it into the layer archive.

Fixes #34137.

pkgs/build-support/docker/default.nix

···
         cp ${layer}/* temp/
         chmod ug+w temp/*
 
-        echo "$(dirname ${storeDir})" >> layerFiles
-        echo '${storeDir}' >> layerFiles
         for dep in $(cat $layerClosure); do
           find $dep >> layerFiles
         done