Run this in a Terminal:

/System/Library/Frameworks/CoreServices.framework/Frameworks/\
LaunchServices.framework/Support/lsregister \
-kill -r \
-domain local -domain system -domain user 

Then relaunch the Finder (Command+Option+Escape, click Finder, click Relaunch).

—Ben Darlow: How to remove duplicate items from the “Open With…” contextual menu in the Mac OS X Finder