The JSON field was added in [moby@9fd2c0f], to address [moby#19177], which
reported an incompatibility with Classic (V1) Swarm, which produced a non-
standard response;
> Make docker load to output json when the response content type is json
> Swarm hijacks the response from docker load and returns JSON rather
> than plain text like the Engine does. This makes the API library to return
> information to figure that out.
A later change in [moby@96d7db6] added additional logic to make sure the
correct content-type was returned, depending on whether the `quiet` option
was set (which produced a non-JSON response). This caused inconsistency in
the API response, and [moby@2f27632] changed the endpoint to always produce
JSON (only skipping the "progress" output if `quiet` was set).
This means that the "load" endpoint ([`imageRouter.postImagesLoad`]) now
unconditionally returns JSON, making the `JSON` field fully redundant.
This patch removes the use of the JSON field, as it's redundant, and the way it handles
the content-type is incorrect because it would not handle correct, but different
formatted response-headers (`application/json; charset=utf-8`), which could
result in malformed output on the client.
[moby@9fd2c0f]: 9fd2c0feb0
[moby#19177]: https://github.com/moby/moby/issues/19177
[moby@96d7db6]: 96d7db665b
[moby@2f27632]: 2f27632cde
[`imageRouter.postImagesLoad`]: 7b9d2ef6e5/api/server/router/image/image_routes.go (L248-L255)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
f594a7f09b