Remove Java files, they cause recompilations

For weir unknown reasons, these Java files are recompiled by Play 2.1 every
time I change e.g. a CSS file or JS file in debiki-server (which uses
SecureSocial as a sub module). This is very annoying because then it takes 10 -
15 seconds more to test every tiny tiny CSS tweak. — But if I remove the Java
files, Play won't be able to recompile them :-)