conformance: remove check for zero layers in image manifest

As per image-spec, since this is a SHOULD (hence recommended) ...

https://raw.githubusercontent.com/opencontainers/image-spec/main/manifest.md

===

layers array of objects

Each item in the array MUST be a descriptor. For portability, layers
SHOULD have at least one entry.

===

Signed-off-by: Ramkumar Chinchani <[email protected]>

conformance/02_push_test.go

@@ -348,20 +348,6 @@ var test02Push = func() {
 				}
 			})
 
-			g.Specify("Registry should accept a manifest upload with no layers", func() {
-				SkipIfDisabled(push)
-				RunOnlyIfNot(skipEmptyLayerTest)
-				req := client.NewRequest(reggie.PUT, "/v2/<name>/manifests/<reference>",
-					reggie.WithReference(emptyLayerTestTag)).
-					SetHeader("Content-Type", "application/vnd.oci.image.manifest.v1+json").
-					SetBody(emptyLayerManifestContent)
-				resp, err := client.Do(req)
-				Expect(err).To(BeNil())
-				location := resp.Header().Get("Location")
-				Expect(location).ToNot(BeEmpty())
-				Expect(resp.StatusCode()).To(Equal(http.StatusCreated))
-			})
-
 			g.Specify("GET request to manifest URL (digest) should yield 200 response", func() {
 				SkipIfDisabled(push)
 				req := client.NewRequest(reggie.GET, "/v2/<name>/manifests/<digest>", reggie.WithDigest(manifests[1].Digest)).