Fix hacky Dropbox's accessibility issue

# Dropbox has a hacky way to take control over your computer without you knowing
# These commands avoid that.
#
# https://news.ycombinator.com/item?id=12463338
# http://applehelpwriter.com/2016/07/28/revealing-dropboxs-dirty-little-security-hack/
# http://applehelpwriter.com/2016/08/29/discovering-how-dropbox-hacks-your-mac/

# 1. Remove executable and suid bits and lock dbaccessperm file.

cd /Library/DropboxHelperTools/Dropbox_u502
sudo chmod -sx dbaccessperm
sudo chflags uchg dbaccessperm

# 2. Remove (just uncheck) accessibility permission for Dropbox via System Settings.