Revert "buildenv: read propagated-user-env-packages line-by-line"

    my $propagatedFN = "$pkgDir/nix-support/propagated-user-env-packages";

    if (-e $propagatedFN) {

        open PROP, "<$propagatedFN" or die;

        while (my $p = <PROP>) {

            chomp $p;

        my $propagated = <PROP>;

        close PROP;

        my @propagated = split ' ', $propagated;

        foreach my $p (@propagated) {

            $postponed{$p} = 1 unless defined $done{$p};

        }

        close PROP;

    }

}