Chore: Remove react-addons-test-utils (styleguidist#625, styleguidist#614)

Author: tizmagik

package-lock.json

@@ -123,7 +123,6 @@
     "preact-compat": "^3.16.0",
     "prettier": "^1.7.0",
     "react": "^15.6.1",
-    "react-addons-test-utils": "^15.6.0",
     "react-dom": "^15.6.1",
     "react-modal": "^2.2.2",
     "react-test-renderer": "^15.6.1",