I stumbled upon this short Lifehacker article about how to clean up duplicate apps listed in the “open with…” contextual menu. It caught my eye because I was just wondering how to clean this up on my Macbook Pro. I have installed Photoshop and then later upgraded so there are now two “photoshop” options listed. Looks like the solution is to rebuild your Mac’s LaunchServices database with the following terminal command.
LaunchServices.framework/Support/lsregister -kill -r -domain local -domain system -domain user