libcamera: thread: Remove the unused setEventDispatcher() function

Custom event dispatchers for threads was an API meant to provide a way
to integrate libcamera in the application's event loop. This isn't used
anymore, as libcamera now creates internal threads. Drop the unused
Thread::setEventDispatcher() function, and update the documentation
accordingly.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

include/libcamera/internal/thread.h

@@ -46,7 +46,6 @@ public:
 	static pid_t currentId();
 
 	EventDispatcher *eventDispatcher();
-	void setEventDispatcher(std::unique_ptr<EventDispatcher> dispatcher);
 
 	void dispatchMessages(Message::Type type = Message::Type::None);