Remove toString-based minification check (#10673)

packages/react/index.js

@@ -1,50 +1,6 @@
 'use strict';
 
-function testMinificationUsedDCE() {
-  if (process.env.NODE_ENV === 'development') {
-    // We expect this method only to be called in production.
-    throw new Error('This is unreachable');
-  }
-  try {
-    // use scoped variable for our initial test, in case
-    // 'top-level' mangling is not enabled.
-    var source = testMinificationUsedDCE.toString();
-    var longVariableName = true;
-    if (longVariableName && source.match(/longVariableName/g).length === 3) {
-      // We are not minified.
-      // This might be a Node environment where DCE is not expected anyway.
-      return;
-    }
-    if (source.match(/toString/g).length !== 2) {
-      // We always look for two matches:
-      // The actual occurence and then the call to 'match'
-      //
-      // We know for a fact the above line exists so there should be 2
-      // matches.
-      // Therefore the browser gave us invalid source.
-      return;
-    }
-    if (source.match(/unreachable/g).length === 2) {
-      // We always look for two matches:
-      // The actual occurence and then the call to 'match'
-
-      // Dead code elimination would have stripped that branch
-      // because it is impossible to reach in production.
-      setTimeout(function() {
-        // Ensure it gets reported to production logging
-        throw new Error(
-          'React is running in production mode, but dead code ' +
-            'elimination has not been applied. Read how to correctly ' +
-            'configure React for production: ' +
-            'https://fburl.com/react-perf-use-the-production-build'
-        );
-      });
-    }
-  } catch (e) {}
-}
-
 if (process.env.NODE_ENV === 'production') {
-  testMinificationUsedDCE();
   module.exports = require('./cjs/react.production.min.js');
 } else {
   module.exports = require('./cjs/react.development.js');