Deletes the event handler represented by the specified event registration token from the set of event handlers associated with the current EventSource object.
A handle that represents an event handler. This token was returned when the event handler was registered by the Add() method.
S_OK if successful; otherwise, an HRESULT that indicates the error.
For more information about the EventRegistrationToken structure, see the Windows::Foundation::EventRegistrationToken Structure topic in the Windows Runtime reference documentation.