Private and old helpers are listed in guides

Under the template tag guide there are listed old and already removed helpers like `with` and `loc`.
There is also `readonly` listed, which is private.

Here a list:
- `with` was deprecates in v3 (https://deprecations.emberjs.com/ember/v3.x/#toc_ember-glimmer-with-syntax)
- `loc` was deprecated in v3 (https://deprecations.emberjs.com/v3.x#toc_ember-string-loc)
- `hasBlock` was replaced with `has-block`
- `readonly` is since begin a private helper so we should remove from guide docs (https://api.emberjs.com/ember/5.8/classes/Ember.Templates.helpers/methods/readonly?anchor=readonly&show=inherited%2Cprivate)

We should remove them for current docs page.

Docs link:
https://github.com/ember-learn/guides-source/blob/master/guides/release/components/template-tag-format.md#keywords