Uh, no. An operator is below admin. "User" is user.
See the big bold question
How do I remove a user? from that link Spbogie provided you.
I don't know how many times we can try to teach this, but I'll throw it in for you, and anyone else that might ever read only this post.
99% of addons will never modify gmod/addons/<insert_any_file_here>
If you look at /gmod/data/ULib (<--- NO ADDONS) , you should find the modified users.txt.
Addons aren't supposed to be able to modify files not in gmod/data