Remove unncessary imports

src/Microsoft.AspNetCore.JsonPatch/project.json

@@ -37,10 +37,7 @@
         "System.Runtime.Extensions": "4.1.0-*",
         "System.Runtime.Serialization.Primitives": "4.1.1-*",
         "System.Text.Encoding.Extensions": "4.0.11-*"
-      },
-      "imports": [
-        "portable-net451+win8"
-      ]
+      }
     }
   }
 }