Power on the AP while holding down the Mode button until the LED turns red, then release.  Wait for the “ap:” prompt.  Then do this:

ap: delete flash:capwap-saved-config
Are you sure you want to delete "flash:capwap-saved-config" (y/n)?y
File "flash:capwap-saved-config" deleted
ap: boot
Rebooting system to reset DPAA...

And for good measure

AP#delete flash:config.txt
Delete filename [config.txt]? 
Delete flash:/config.txt? [confirm]
Proceed with reload? [confirm]