Remove unused babel class plugin

Author: oliverjam

.babelrc

@@ -1,4 +1,3 @@
 {
-  "presets": ["@babel/preset-env", "@babel/preset-react"],
-  "plugins": ["@babel/proposal-class-properties"]
+  "presets": ["@babel/preset-env", "@babel/preset-react"]
 }

package.json

@@ -21,7 +21,6 @@
   "homepage": "https://github.com/oliverjam/learn-react-testing#readme",
   "devDependencies": {
     "@babel/core": "^7.2.2",
-    "@babel/plugin-proposal-class-properties": "^7.3.0",
     "@babel/preset-env": "^7.3.1",
     "@babel/preset-react": "^7.0.0",
     "@testing-library/react": "^9.1.4",
@@ -33,4 +32,4 @@
     "react-dom": "^16.9.0-alpha.0",
     "whatwg-fetch": "^3.0.0"
   }
-}
+}