Remove scheduler from React package dependencies (#15616)

Scheduler is used by the renderers, but not the isomorphic package.

Author: acdlite

packages/react/package.json

@@ -28,8 +28,7 @@
   "dependencies": {
     "loose-envify": "^1.1.0",
     "object-assign": "^4.1.1",
-    "prop-types": "^15.6.2",
-    "scheduler": "^0.14.0"
+    "prop-types": "^15.6.2"
   },
   "browserify": {
     "transform": [