Remove old plugin system

Remove the old client/instance fused plugin system along with
instanceManagement in client.js and getPlugins in master.js.

package.json

@@ -65,7 +65,6 @@
     "socket.io-client": "^2.2.0",
     "socket.io-prometheus": "^0.2.1",
     "sync-request": "^4.0.1",
-    "tail": "^2.0.2",
     "typescript-collections": "^1.3.2",
     "yargs": "^14.2.0"
   },