Remove meaningless fields from ChangeFeedStatus

[CharlesCheung96]

ChangeFeedStatus will not be read by the processor in the future, so the processor should not rely on its fields

https://github.com/pingcap/tiflow/blob/master/cdc/model/owner.go#L279

e.g.: processor manager currently relies on AdminJobType:
https://github.com/pingcap/tiflow/blob/master/pkg/orchestrator/reactor_state.go#L243-L245