libcamera: request: Store fence EventNotifier directly

Simplify a bit by storing the `EventNotifier` objects directly in the
`std::map` instead of wrapping them in unique_ptr. An other advantage
is that it removes one allocation per fence.

Signed-off-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>

include/libcamera/internal/request.h

@@ -59,7 +59,7 @@ private:
 	bool prepared_ = false;
 
 	std::unordered_set<FrameBuffer *> pending_;
-	std::map<FrameBuffer *, std::unique_ptr<EventNotifier>> notifiers_;
+	std::map<FrameBuffer *, EventNotifier> notifiers_;
 	std::unique_ptr<Timer> timer_;
 };