build: dgeni is building docs twice (#5536)

* With #5429 dgeni runs twice when running the `gulp docs` command. This is because the dgeni generate function has been added to the `dgeni/index.js` file.

Author: devversion

tools/dgeni/index.js

@@ -156,7 +156,3 @@ let apiDocsPackage = new DgeniPackage('material2-api-docs', dgeniPackageDeps)
 
 
 module.exports = apiDocsPackage;
-
-
-  const docs = new Dgeni([apiDocsPackage]);
-  docs.generate();