refactor: remove unused spack.stage._get_mirrors() function
refactor: remove unused spack.stage._get_mirrors() function

LLNL/spack,iulian787/spack,iulian787/spack,iulian787/spack,LLNL/spack,iulian787/spack,LLNL/spack,LLNL/spack,LLNL/spack,iulian787/spack