docker/types.go: remove unused struct fields
docker/types.go: remove unused struct fields

Reported by golangci-lint.

Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

Closes: #1624
Approved by: TomSweeneyRedHat

projectatomic/buildah,TomSweeneyRedHat/buildah,nalind/buildah-1,TomSweeneyRedHat/buildah,projectatomic/buildah,nalind/buildah-1,TomSweeneyRedHat/buildah,nalind/buildah,nalind/buildah,projectatomic/buildah,rhatdan/buildah,rhatdan/buildah,rhatdan/buildah,nalind/buildah-1