Many OEMs recommend replacement of the abutment clips with each pad change. A genuine Subaru pad set comes with the abutment clips. The reason why your pads were stuck in the bracket is because of rust buildup between the bracket and the clip. You will likely need something more aggressive than a wire wheel to clean it. I usually use a scotchbrite disc on a die grinder or a file to clean the bracket to bare metal
On reassembly, coat the area of the bracket that the clips sit on with brake grease to help prevent corrosion. Install the clips, then a layer of grease on top for the pads to slide on. We use AC Delco silicone brake grease.