Dialogue System Event Subscriptions Not Being Removed

[kgc00]

Short description
Current PR for dialogue system subscribes / unsubscribes from events using lambdas. This is unreliable and will cause bugs to pop up. More reading: https://stackoverflow.com/questions/1362204/how-to-remove-a-lambda-event-handler
multiple plays of cutscenes should see us subscribed to old playable directors and / or subscribed multiple times to the input system events.

Expected behaviour
Should be subscribed once and only once to each event.

To Reproduce
Steps to reproduce the behavior:

1. put a log statement in the event delegate
2. trigger multiple cutscenes
3. see multiple calls of the same function

Notes

• https://forum.unity.com/threads/dialogue-system-timeline-track.980712/page-2#post-6507001