compliance/tests: drop Comment check from valid_image rego rule

The moby/moby v29 SDK (introduced in #48777) changed
image.InspectResponse.Comment from a plain string field to
`json:",omitempty"`. Images built without an explicit comment (e.g.
ubuntu:24.04) now omit the key from JSON, causing has_key to return
false.
This was hidden from the CI because the test skips when it can't connect
to the docker socket, which will happen in our CI env

Author: chouquette

pkg/compliance/tests/docker_test.go

@@ -136,7 +136,6 @@ valid_image(i) {
 	has_key(i, "id")
 	has_key(i, "inspect")
 	has_key(i.inspect, "Architecture")
-	has_key(i.inspect, "Comment")
 	has_key(i.inspect, "Config")
 }