Delete duplicated docs folders (#3780)

# Description of Changes

Somehow (apparently after #3494) we wound up with a bunch of duplicate
folders in our repo, both the old title-case names and the new
lower-case names. All of the remaining files in the title-case
directories have their last change in #3343, well before #3494, so I
don't believe we're losing any intermediate changes by deleting them.
I'm not sure how this happened, but it seems to be an easy fix.


# API and ABI breaking changes

N/a

# Expected complexity level and risk

2 - some small possibility that I accidentally deleted an intentional
change that got borked by a merge conflict or something. I don't think I
did, tho, based on the age of the git blame on the files deleted here.

# Testing

None

Author: gefjon