I know it is old topic but I had same problem with Opera 12.16, and posting this here for someone who is having same problem.
I tryed to completely remove opera with
sudo apt-get purge opera
with Synoptic Package Manager
But they didn't remove all its file. With Opera 12.16 all its extra files are in you home directory .opera
folder. If you delete this then you are comletley free from opera