ipatests: remove xfail for test_ipa_migrate_stage_mode
    
    The test test_ipa_ipa_migration.py::TestIPAMigrateScenario1
    ::test_ipa_migrate_stage_mode is now passing, the issue has been fixed.
    
    Related: https://pagure.io/freeipa/issue/9621
    
    Signed-off-by: Florence Blanc-Renaud <flo@redhat.com>
    Reviewed-By: Sudhir Menon <sumenon@redhat.com>