You need to get to ~/Library/Preferences/, you can get there with the Go to Folder Command+Shift+G option, or by the instructions below:Open your Home directoryOpen the “Library” folderFind and open the “Preferences” folderOnce you are in the proper folder:Locate “”Rename “” to “” or just relocate it elsewhere you can delete it completely if you aren’t worried about backupsNow the next time you use the “Open With” menu it will only include current applications in the list. You may need to log in and out of your user account for changes to take effect.The Open With menu is fairly adjustable in its default behavior, you can also learn how to change a file types association across the board or on a per file basis for more specific files.

via Clear the “Open With” menu in Mac OS X.