I first attempted to use 'find' to create a one line command to rename all of these folders, but it turns out bash for and do were the answer, thusly:
for file in *; do mv "$file" "${file%???}"; done
The syntax for doing the trimming came from this thread (although sadly the pythonesqe method of trimming with colons and a negative end position didn't work in cygwin bash for some reason): https://stackoverflow.com/questions/19530429/rename-file-by-removing-last-n-characters
The example of using for/do came from here: https://stackoverflow.com/questions/7450818/rename-all-files-in-directory-from-filename-h-to-filename-half