make-initrd: drop unused `toValidStoreName` local (#482823)

    _compressorMeta.ubootName

      or (throw "Unrecognised compressor ${_compressorName}, please specify uInitrdCompression"),

}:

let

  # !!! Move this into a public lib function, it is probably useful for others

  toValidStoreName =

    x: with builtins; lib.concatStringsSep "-" (filter (x: !(isList x)) (split "[^a-zA-Z0-9_=.?-]+" x));

in

stdenvNoCC.mkDerivation (

  rec {

    inherit