My b2evolution Version: 1.8.x

Greetings, I was looking to find out how to remove some options from the filter search on the post tab in these sub tabs (post list, tracker, full posts). On the right hand side there is a Filters search. Under that there is Assignees and Authors to choose from. I would like to remove those options so people can't pick them. I'm not sure what file to find that in. If someone could help me out I appreciate it.

Thanks,
~webjoker