Remove existing `session.set_status('running')` status changes in agents

[BrianJKoopman]

As of ocs v0.11.0 the session status is automatically changed to 'running' just before operations are called, so this no longer needs to be called explicitly in the agents. Doing so might lead to rare instances of calling session.set_status('running') after the state has already moved on, if for instance, a stop() or abort() is called before the status 'running' call is made. This would raise an error as the status cannot move backwards, as pointed out here.