[Icemaster]

I did this a few mos ago. Your setup looks almost identical to mine less the dry set wall.

I cut them ~3 inches from flush to the concrete surface, put an auger bit in the drill and drilled out series of holes down the centerline running north --> south and east-->west, cleaned a little with a chisel for a (mostly) clean slot, took a 5 lb sledge and knocked the 4 sections inward one at a time, pulled them out mostly intact.

Once the first piece comes out the rest are easy. Trick is to get all the way down to the bottom of the post.