vshReadlineParse: Drop code duplication
    
    Now that we have a way of retrieving partly parsed command we
    don't need duplicate code that parses the user's input.
    
    Yes, this code removes call of opt's completer, but:
      a) current implementation is broken anyway, and
      b) it will be added back shortly
    
    Signed-off-by: Michal Privoznik <mprivozn@redhat.com>