Updated Packages/manifest.json to load Animation Rigging from Package Manager instead of a local copy.

Packages/manifest.json

 {
   "dependencies": {
-    "com.unity.animation.rigging": "file:../../com.unity.animation.rigging",
+    "com.unity.animation.rigging": "0.2.2-preview",
     "com.unity.burst": "1.1.1",
     "com.unity.collab-proxy": "1.2.16",
     "com.unity.ext.nunit": "1.0.0",