Ran wesnoth-optipng on the new Dutch images:

Overall statistics (only for files with a smaller recompressed size):
  Original size: 65 KiB on 1 files
 Optimized size: 63 KiB
   Total saving: 2 KiB = 4% decrease


git-svn-id: http://svn.gna.org/svn/wesnoth/trunk@56205 75b3775d-3801-0410-9e12-e2e43121521d