The F1AP UE context release procedure can happen in at least two cases:

1. core requested a release of a UE
2. CU requests DU a release of a UE without a core release (e.g.,
   handover)

In case 1., the CU has to fully release the UE in the CU, then ack the
NGAP message from the core, whilst in 2., nothing of that should happen
after the DU acknowledges the F1AP UE context release cmd.