White Phosphorus
The temperature at which bone is burnt to ash is around 1600 degrees Celsius. White Phosphorus burns vigorously when exposed to air, is sticky, and burns hotter than thermite, at around 2760 degrees Celsius (5000 degrees Fahrenheit). I am fairly certain WP munitions will make short work of skeletons. I tried to look up how long it would take their bones to burnt to ash, but couldn't really find anything.
Just don't use it close to you or in any building that could burn down. And don't breathe the fumes; repeated exposure is known to make your jawbone dissolve.
Edit: Other extreme heat technologies
It has been pointed out that WP burns at 5K Farenheit, not Celsius. That error means WP is only 1000 degrees above the decomposition temperature of bone, which may not be fast enough.
Either of these two burn much hotter:
A MIG welder requires power and a gas supply, which imposes limitations on its use. But it produces a plasma stream which ranges between 6 to 24 thousand degrees Celsius. Even with full-on welders' gear, I wouldn't want to try to fight hand-to-hand with one, but channel your inner Kevin McAllister and set up point defense booby-traps.
Booby traps involving a combination of dicyanoacetylene (burns at 5000 Celsius) to be set off via conjuring some liquid oxygen from... As far away as you can get would probably be enough to get rid of your skeleton problem. They might also start an inferno that gets rid of much of the town.
Edit: Incendiaries have a big drawback
Basically, you can, if you look hard enough, find incendiaries we either have today, or could figure out how to make (if we needed it desperately enough) that are energetic enough to destroy a bone skeleton quickly enough to save the day. The problem is anything vigorous enough to do the job will necessarily pose an extreme fire hazard to anything flammable, specifically to wooden buildings. Even dust-grain sized droplets of burning dicyanoacetylene, or liquid oxygen, can land on tinder and there's a good chance your hero is going to have a bad day. And the skeletons will likely thrash around enough to cause such spraying.
Works great in stone buildings. Wood buildings, not so much.
