Removing Mathias' dotfiles settings
There is no simple command to revert everything to default.

Depending on the number of installed apps besides Apple's own standard apps, it's probably faster to reinstall OS X or restore a backup.

.osx alone modifies about 200 settings - assuming one mod per 4 lines.

Next time better use a hypervisor like VMware or Virtual Box, set up your preferred OS X in a VM and test dotfiles using the snapshot feature.