Similar to EventEmitter.prototype.removeListener()
Detach all handlers from the Evt or all Evt's handler that are bound to a given context.
The prefered way of detaching handler in TS-EVT is via Ctx<T> .
Calling this method without passing a context argument is almost never a good idea. An Evt instance should be sharable by modules that are isolated one another. If a module take the liberty to call evt.detach() it can brek the code elswhere.