To release a tiny screw from a threaded partially blind hole — I removed front sight blade from its base on barrel — I put a drop of Kroil® in the hole atop the screw and let it work for a few days to loosen locktite-type material. The screw is so small and its hexhead is so small that I feared stripping the head.

To install a front sight blade and secure it in place, how do I remove all trace of Kroil?

Xylene.
I have but one experience with Kroil; in a bear camp many years ago, a guy had his rifle bathed in the stuff; at least that is what it smelled like. You could smell it from 20 feet away. I told him no bear would get within 50 yards of him.
None did.

acetone

MEK. Acetone evaporates too fast to penetrate. MEK works like Acetone but doesn't evaporate as fast.
George