chore: drop ts/_cache (#2974)

* chore: drop dart cache and link check scripts

* chore: delete ts/_cache

* chore(README): remove mention of ts/_cache

* chore: ignore ts/_cache files

Author: chalin

.gitignore

@@ -33,4 +33,5 @@ protractor-results.txt
 link-checker-results.txt
 *a2docs.css
 /dist
-/public/docs/dart
+/public/docs/dart
+/public/docs/ts/_cache

README.md

@@ -21,8 +21,6 @@ Filing issues is helpful but **pull requests** that improve the docs are even be
 
 Learn how to [contribute to Angular.io](https://github.com/angular/angular.js/blob/master/CONTRIBUTING.md).
 
-> **IMPORTANT**: Do _NOT_ make changes to cached files under `public/docs/ts/_cache`. Cached files are updated through a separate workflow.
-
 ## Development Setup
 This site relies heavily on node and npm.