Just click "edit" on the page, and then go to the bottom right-hand corner. All the categories of the page are listed there. Put your mouse over a category, and there's an icon that shows a little trash can. Click on that, and it removes the category.
Welp, I'm gonna try and send a notice to Wikia about PhazonGumball. But in addition to him, I'm wondering about some of the other users. I wanted to ask your opinion before I send in the notice:
Anthurium (Founder, inactive since 2008, last login: 2008; not sure what to do about him, considering he is the founder of the wiki. Maybe give him a special headmast thing on their profile page like we have for Wack'd About Wikia on the LT Wiki?)
Ivanovsson (inactive since 2008, last login: 2009)
Stealthghost (inactive since 2011, last login: 2013)
Also, could you please remove Thatguyfromuae's rollback rights? :P
Could you remove his admin rights? He's only made one edit here and I'm not quite sure why he has these rights. I plan on contacting Wikia about removing his b-crat rights as well, if that's ok with you. :)
No offense, but there sure is a lot of matience work to be done here. Lot's of duplicate categories, duplicate pages, etc. I'm gonna try and help this wiki out as best I can, if that's alright with you. :)