Remove Spark Operator AppManager

For some time, YuniKorn has supported a configurable AppManager interface. However, there are only two implementations:

• general: used for general application management (maps via applicationID)
• spark-k8s-operator: mapping via spark operator

This interface has grown in complexity over time, but is not used consistently within the code base. Disabling the general AppManager results in a broken scheduler, as pods do not map correctly. Additionally, the spark-k8s-operator AppManager is only used in non-default configurations and only maps Spark Application completion state onto YuniKorn application completion state via calling NotifyApplicationFail() or NotifyApplicationComplete(). This can conflict with the normal processing of these events and lead to failures.

To simplify and eventually eliminate the AppManager abstraction, we should remove the spark-k8s-operator AppManager entirely. No functionality will be lost (except for a questionable mapping between spark app success/fail and yunikorn app success/fail). This mapping is questionable anyway as there is no real concept of Application success in Kubernetes, so it is not used in the vast majority of cases.