Revert "initial perf, which gets stripped out in production (#4131)" (#4636)

This reverts commit 5ea2150ae7.

webpack-dist.config.js

@@ -15,17 +15,7 @@ let rules = [
       },
       { loader: "babel-loader?retainLines=true" }
     ]
-  },
-  // This will strip out blocks of code that start with:
-  /* develblock:start */
-  // And end with
-  /* develblock:end */
-  {
-    test: /\.jsx?$/,
-    enforce: "pre",
-    exclude: /(node_modules|\.spec\.js)/,
-    loader: "webpack-strip-block"
-  },
+  }
 ]
 rules = rules.concat(styleRules)