FWIW, some observations I've made with Wordpress sites:
--Adding social media buttons never seems to affect rankings
--Adding a "recent posts" plugin sometimes does, and I've never figured out why.
I haven't used that Facebook plugin. I really don't know how the bot would react to those lines of code it added - it could just ignore them, or it could decide there's an issue. I would suggest looking for another FB plugin that gives you similar functionality without the code bloat, and then you'll have solved that "problem" whether it really was a problem or not.