Ed is right that any grinder for concrete will handle thinset. However I doubt that the thinset is grindable.
When thinset goes onto concrete there is no molecular bond that causes the thinset to stick permanently to the concrete. In fact it expands and contracts at different rate as concrete so it is actually "moving" all the time.
Thinset works because of this. It "sticks" because the thinset sticks well to itself and so the bind of the thinset really keeps it in place. Yes it may kind of stick to the concrete, but not that well once you start breaking it apart.
Meaning if you start grinding it, sure some parts will grind down well but others, the thinset will just pop out of place - meaning your floor will have divots.
The best course of action is to jsut knock all of the thinset loose which can be done with a mallet or hammer just tapping the thinset straight down hard. You don't want to take swings as you will nick the concrete. The thinset will come up quickly like this. Note if you just leave thinset on the concrete it will all eventually come loose after walking directly on it.
After you are done removing thinset you can fill in any gaps or use leveler to make the surface more livable. However thinset is not an option here because as noted before it does not bind well with concrete. I have taken thinset/tile out of more the my share of bathrooms with concrete floors and the concrete looked practically brand new after I was done.
