Remove outputs from the yaml files

The latest version of the `moby` tool now requires that the output formats
be specified in the CLI not in the yaml file.

Signed-off-by: Justin Cormack <justin.cormack@docker.com>

projects/okernel/examples/okernel_simple.yaml

@@ -26,7 +26,3 @@ services:
 files:
   - path: root/.ssh/authorized_keys
     contents: '#your ssh key here'
-outputs:
-  - format: kernel+initrd
-  - format: iso-bios
-  - format: iso-efi