dracut: remove workarounds for broken splitsep()
    
    the splitsep function was buggy before, but it was fixed in dracut 019
    so we don't need these workarounds anymore.
    
    See upstream dracut commit f7cadaa843498c4b986f8a030fab39002ad108b6.
    
    Related: 844c0c156ed2f27920257d86690f3017727f398e
    Related: 700e985082b03abcbd3009de81885b8fbf72818b