Remove some unused resource files

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>
JacksonUtils: get rid of .emptyObject()

It was mostly used for getting an empty schema for keywords which needed it in
the previous API. But the new API does not need it anymore.

Remove it, and replace the only one use of it in tests.

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>