This validation is now handled by the API-client since [moby@5d6b566],
so no longer needed to be done in the cli. This function was only used
internally and has no external consumers, so removing it without
deprecating first.
[moby@5d6b566]: 5d6b56699d
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>