How can I remove Cordova and ionic installation from my Mac completely? I am running mac os Yosemite 10.10.2
BlueBell's answer is right, you can do it by:
npm uninstall cordova ionic
Are you planning to re-install it? If you feel something's wrong which is causing problems then you should update npm and clean npm's cache.
npm cache clean -f npm install npm -g
If problems still persist, I'd suggest re-install of NPM and Node.
npm uninstall node apt-get purge npm apt-get install npm npm install node -g
Let me know if you face issues in the process.