Remove jupyter-js-widgets lab extension for now because it uses old phosphor repos.

jupyterlab/package.json

@@ -8,7 +8,6 @@
   "dependencies": {
     "es6-promise": "^3.1.2",
     "font-awesome": "^4.6.1",
-    "jupyter-js-widgets-labextension": "^0.1.0",
     "jupyterlab": "file:../",
     "material-design-icons": "^2.2.3"
   },