Here is the list of MIMEs and associated applications (for all users):
User created (added) applications are stored here:
The best way to remove application from "Open with" would be to edit corresponding application.desktop and remove the MIME from the MimeType section. And after that do
Files .desktop are stored in two locations:
Ok, the easy way. By 'easy' I mean - it's working but if you run update-desktop-database the list is reverted back to defaults.
gksudo gedit /usr/share/applications/mimeinfo.cache