Removed unneeded .Net Core reference

src/Discord.Net/project.json

@@ -41,7 +41,6 @@
       "dependencies": {
         "System.Collections": "4.0.11-beta-23516",
         "System.Collections.Concurrent": "4.0.11-beta-23516",
-        "System.Dynamic.Runtime": "4.0.11-beta-23516",
         "System.IO.FileSystem": "4.0.1-beta-23516",
         "System.IO.Compression": "4.1.0-beta-23516",
         "System.Linq": "4.0.1-beta-23516",