Hi Mike,
new one on me...
...not sure apart from deleting the Apps that are no longer required
You could change the settings globally so that whenever you click on a ".png" it always opes with Application "X" then that should save you going to the open with list for most of your images.
Say if you do alot of screen grabs, which are ".png" files, these by default always open in Preview, but if for 90% of the time you know that you are going to open ".png" files in another Application, and so always have to right click (control click for the old School ;-) then the easiest way is to select 'any' ".png" file and press command + i then in the info box change the open with "to the Application" that you want, and press the "Change All" button...
Now when ever you double click on a ".png" file it will always open in Application "X" and not in preview...
Are the 'duplicates' Applications, ones that you 'still' have on your drive ? Or has the Application been removed ?
regards
Ric