Implement Delete in the oci store content implementation (#174)

Signed-off-by: viovanov <vlad@aserto.com>

pkg/content/oci.go

@@ -276,10 +276,9 @@ func (s *OCI) Walk(ctx context.Context, fn content.WalkFunc, filters ...string)
 	return errors.New("not yet implemented: Walk (content.Store interface)")
 }
 
-// TODO: implement (needed to create a content.Store)
 // Delete removes the content from the store.
 func (s *OCI) Delete(ctx context.Context, dgst digest.Digest) error {
-	return errors.New("not yet implemented: Delete (content.Store interface)")
+	return s.Store.Delete(ctx, dgst)
 }
 
 // TODO: implement (needed to create a content.Store)