ok.. It is two years now since you posted your inquiry hahahha. Here is the answer if you still need it, otherwise, it will always be here to tot he rest of the world.
Remove Twixtor 5.04 from After Effects CS5.5 on MAC OS X 10.7 (Lion):
Step 1: close After Effects
Step 2: Open Finder
Step 3: open Macintosh HD (here is how i do it: click on finder> press and hold command key and keep pressing the up arrow on keyboard until you see Macintosh HD icon.
Step 4: follow this path: Library/Application Support/Adobe/Common/Plug-ins
Step 5: after opening the Plug-ins folder, look for the folder pointing to the version of After Effects you have on your MAC and open it, in my case it is CS5.5
Step 6: open the folder named Media Core
Step 7: look for a folder named Twixtor and guess what “Delete the bastard”.
Step 8: Never give up if you fail to do something 🙂
Thanks