ot::Srp::Client::RemoveService() method

A `Service` to remove (the instance must persist and remain unchanged after successful return from this method).

Adds a service to be registered with server. After a successful call to this method, `Callback` will be called to report the status of the service addition/registration with SRP server.

Clears a service, immediately removing it from the client service list. Unlike `RemoveService()` which sends an update message to the server to remove the service, this method clears the service from the client's service list without any interaction with the server. On a successful call to this method, the `Callback` will NOT be called and the @p aService entry can be reclaimed and re-used by the caller immediately.