Uninstalling MySQL Community Server on OS X Revision as of Sunday, 20 December 2015 at 19:56 UTC
Tested on 10.7 (Lion) and 10.6 (Snow Leopard).
Remove all startup items, receipts and the MySQL installation directory:
sudo rm -rf /Library/StartupItems/MySQL*
sudo rm -rf /Library/PreferencePanes/MySQL*
sudo rm -rf /Library/Receipts/mysql-*
sudo rm -rf /var/db/receipts/com.mysql.*
sudo rm /usr/local/mysql
sudo rm -rf /usr/local/mysql-*
Remove this in /etc/hostconfig
MYSQLCOM=-NO-
Done.