We only really support the 'plain' type. Remove all the conditions on image type and remove 'plain' from all target and file names.
The template file has been moved, but POTFILES.in hasn't been updated following that move. This way the po files can be updated using: debconf-updatepo --podir=debian/templates/po svn path=/dists/sid/linux/; revision=21518
svn path=/dists/trunk/linux/; revision=20505