Same boat here. Thought it would be awesome to have facebook app installed and interact with the system, but ever since then had double entries for birthdays and reminders popping up left and right for those and facebook events to the point where its hard to fall asleep at night cos of the constant (and yet random) pinging for reminders for things I have no intention of attending just because its on my facebook social calendar (and yes, maybe I have a few too many "friends").
2 things, before some of you come up with clever remarks; no I will not leave my phone on silent at night because some friends and both parents live in different time zones and I would like to know that they can reach me, especially in an emergency, & no I'm not going to go through my calendar and remove events I will not be attending (especially public ones) because a) I like to know when they are, just in case I change my mind (or come up with a good excuse) b) I never had to do anything before, and for many years, why should I now.
Obviously the double entries I took care of by deleting my birthday calendar from live/outlook/online/whatever its called these days, but this means the full on onslaught of birthday reminders persist and the only way to get rid of them is to disable facebook birthdays and events in the wp8.1 calendar settings. But then I lose my events.
So for the time being the only alternative is to have birthdays synced with live/outlook/hotmail/whats-its and have the facebook app sync the events, thereby reducing the number of reminders popping up just for the hell of it.