qemu: Move vm->persistent check into qemuDomainRemoveInactive
    
    So far we have the following pattern occurring over and over
    again:
    
      if (!vm->persistent)
          qemuDomainRemoveInactive(driver, vm);
    
    It's safe to put the check into the function and save some LoC.
    
    Signed-off-by: Michal Privoznik <mprivozn@redhat.com>