well, i had this problem as well. but the metal ring piece you have circled BROKE on me when i was trying to remove it.
put tape around the area of the antenna and just drill that bitch out. that's what i ended up having to do. the ring broke for me, and it didn't release it from the assembly. so i just took out the old black and decker drill and went at it. ten minutes, and a lot of plastic and rubber shavings later, it was gone. plugged it with a plug and never looked back.
since the car has been at the body shop, they pulled the plug and welded the hole shut. now it looks like it was never there