remove react-is (#23073)

Part of #1265

Author: Peter Bengtsson

package-lock.json

@@ -66,7 +66,6 @@
     "rate-limit-redis": "^2.1.0",
     "react": "^17.0.2",
     "react-dom": "^17.0.2",
-    "react-is": "^17.0.2",
     "react-markdown": "^7.1.0",
     "react-syntax-highlighter": "^15.4.4",
     "redis": "^3.1.2",