Clear out the .git history

[sdellis]

The git history is left over from 2016 and is making the repo gigantic.

[queryluke]

Found this

I'm not a git guru, I hesitate to do something like this unless it's sanctioned by others

[phette23]

Stuff like this is really dangerous and we should probably put off until a relatively slow time (e.g. after proposals & voting are over).