'ctl delete_shovel': adapt to rabbit_shovel_dyn_worker_sup_sup public API changes

[ikavgo]

rabbit_shovel_dyn_worker_sup_sup doesn't export stop_and_delete_child

It exports stop_child which in turn calls stop_and_delete_child.

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[michaelklishin]

The current command still does work because

1. It clears the runtime parameter
2. The result of the "try stopping child" function is ignored

But I agree that if the interface has changed so must the CLI command.