Teardown manifests by digests

Performing a teardown by tag requires support for a 400 (bad request) response.
The test tag is populated with manifest 4 which was already deleted, so remove the tag from the teardown.

Signed-off-by: Brandon Mitchell <[email protected]>

Author: sudo-bmitch

conformance/03_discovery_test.go

@@ -392,7 +392,6 @@ var test03ContentDiscovery = func() {
 						manifests[4].Digest,
 						refsManifestAConfigArtifactDigest,
 						refsManifestALayerArtifactDigest,
-						testTagName,
 						refsManifestBConfigArtifactDigest,
 						refsManifestBLayerArtifactDigest,
 						refsManifestCLayerArtifactDigest,
@@ -453,7 +452,6 @@ var test03ContentDiscovery = func() {
 						manifests[4].Digest,
 						refsManifestAConfigArtifactDigest,
 						refsManifestALayerArtifactDigest,
-						testTagName,
 						refsManifestBConfigArtifactDigest,
 						refsManifestBLayerArtifactDigest,
 						refsManifestCLayerArtifactDigest,