Personally, I don't know of a quick-and-easy way to remove paint from brick. BUT, if you find one, let us know because you'd make a lot of dreams come true if you do!
Frankly, it's good you want to reverse what's been done. BUT, before you begin, there's something you should 'educate' yourself about. And that is, how brick works. This is important because your methods and such hinge on not damaging the brick to the point where it's permanently damaged. So, for your benefit, and others, here's an old Follow-up I wrote that (among other unrelated stuff) speaks about how brick works.