remove unused fields from executor

these are pre-runoncehandler

Signed-off-by: Ted Young <tyoung@pivotallabs.com>
cancel runonces when failing to maintain presence

This makes .Handle a synchronous API. It will return an error if we fail to
maintain presence, which will bubble up to main and be logged and cause the
executor to exit.

Signed-off-by: Ted Young <tyoung@pivotallabs.com>