Remove vestiges of recursive step execution from AbstractOperationContext

AS 7 supported a recursive mode of operation execution, where an OperationStepHandler would invoke a completeStep() method on the OperationContext and the OC would implement that by finding the next step and executing that. Result was a potentially very deep stack, e.g. during boot which has a lot of steps.

Because of the deep stack issue we implemented a non-recursive mode, and eventually removed support for the recursive mode from the OperationContext API.

But AbstractOperationContext still has code for the recursive mode; this task is to clean that out. It's a source of possible bugs, e.g. flaws in my initial attempt to implement WFCORE-787.