test.go: delete mediatype

Signed-off-by: zhouhao <[email protected]>

Author: zhouhao

schema/manifest_backwards_compatibility_test.go

@@ -52,7 +52,6 @@ func TestBackwardsCompatibilityManifestList(t *testing.T) {
 			digest: "sha256:219f4b61132fe9d09b0ec5c15517be2ca712e4744b0e0cc3be71295b35b2a467",
 			manifestlist: `{
    "schemaVersion": 2,
-   "mediaType": "application/vnd.docker.distribution.manifest.list.v2+json",
    "manifests": [
       {
          "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
@@ -139,7 +138,6 @@ func TestBackwardsCompatibilityManifest(t *testing.T) {
 			digest: "sha256:888206c77cd2811ec47e752ba291e5b7734e3ef137dfd222daadaca39a9f17bc",
 			manifest: `{
    "schemaVersion": 2,
-   "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
    "config": {
       "mediaType": "application/octet-stream",
       "size": 3210,