libraw: drop freeimage from passthru.tests

It's marked as insecure, which is presumably why
the bot thinks that tests wouldn't pass.

pkgs/by-name/li/libraw/package.nix

···
   '';
 
   passthru.tests = {
-    inherit imagemagick hdrmerge freeimage;
+    inherit imagemagick hdrmerge; # freeimage
     inherit (python3.pkgs) rawkit;
   };