build: remove gulp publish tasks (angular#14594)

* The gulp publish script has been replaced with a standalone NodeJS script. This just made a lot of things easier and also could work with Bazel in the future.

Author: devversion

tools/gulp/gulpfile.ts

@@ -28,7 +28,3 @@ import './tasks/lint';
 import './tasks/material-release';
 import './tasks/unit-test';
 import './tasks/universal';
-
-import './tasks/publish/publish-task';
-import './tasks/publish/sanity-checks';
-import './tasks/publish/validate-release';