Remove Crouton from Chromebook for Fresh Install

https://github.com/dnschneid/crouton/issues/10

Yep. It's probably easiest to let crouton do the checking for you, though:
cd /usr/local/chroots && sudo delete-chroot -y * && rm -rf /usr/local/bin
but if you're curious, you can confirm there are no lingering bind mounts via mount | grep ' /usr/local/chroots/'