I've never tried to destroy provincial AA. Maybe something to experiment with for a day or two. My first idea would be planes on installation bombing missions. I've never really used the installation bombing missions. I'm guessing that these missions should damage built province improvements (air fields, naval bases, infrastructure, factories, coastal forts, land forts, AA guns, radar sites, rocket sites and nuclear reactors). I have no idea on target priority, though, and finding an enemy to test it on might be rather difficult. Maybe level 4+ in every category in order to see anything about the priority of targets. Also, is there any inherent difference between Tactical bombers and Strategic bombers -- I could easily imagine a programmed bias to keep Strategic bombers from becoming overpowered vs. units. Also, there are 4 bombing mission types to experiment with -- Strategic Bombing, Logistical Bombing, Airport Cratering and Installation Strike. I'm guessing (again) that these various missions target specific improvement types.
But, it is almost a certainty that destroying AA (or forts) presumably to improve an attack on a province would take too much air power and take far longer than simply making the attack with the defenses in place.