It seems like moving my mesh to 2.8 is making it do some really bizarre stuff. For example, I had a mirror modifier that worked exactly as intended in 2.79 but now when I go into edit mode, modifier still on mind you, I can freely select all vertices on both sides of the mesh. When I delete some vertices thinking that it somehow duplicated the mesh I just see another mesh beneath it in object mode. but when I go back into object mode and move my mirrored mesh to see if there is another one under it, there isn't, and I'm just stumped at whats going on.
It looks like the mesh in the .blend file is already mostly symmetrical, so it shouldn't need a mirror modifier. Anyways, if you want to fix this, simply select all of the vertices left of the center (facing the mesh, it's the character's right) and delete faces (x > f). Then you'll have what you want.