conf: Drop virDomainJobOperation parameter from virDomainObjIsPostcopy

conf: Drop virDomainJobOperation parameter from virDomainObjIsPostcopy

The parameter was only used to select which states correspond to an
active or failed post-copy migration. But these states are either
applicable to both operations or the check would just paper over a code
bug in case of an impossible combination of state and operation. By
dropping the check we can make the code simpler and also reuse existing
virDomainObjIsFailedPostcopy function and only check for active
post-copy states.

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>