If you have previously installed LTTR/INK manually or with the Extension Manager, this is the recommended safety way to uninstall the plugin without hassle.
Open Anastasiy's Extension Manager
In the left menu select Adobe Illustrator
Within the "Extensions" list select LTTR/INK
Click "Remove"
Wait until the dialogue window announces the successful removal.
Click "Done" to close dialogue window
That's it. You have successfully uninstalled the LTTR/INK plugin.