Remove code for rendering public and hashtag timelines outside the web UI (#19257)

app/controllers/directories_controller.rb

app/controllers/public_timelines_controller.rb

app/controllers/tags_controller.rb

app/helpers/application_helper.rb

...pt/mastodon/features/standalone/hashtag_timeline/index.js

...ipt/mastodon/features/standalone/public_timeline/index.js

app/javascript/packs/about.js

app/models/form/admin_settings.rb

app/views/about/show.html.haml

app/views/admin/settings/edit.html.haml

app/views/directories/index.html.haml

app/views/layouts/public.html.haml

app/views/public_timelines/show.html.haml

app/views/tags/_og.html.haml

app/views/tags/show.html.haml

config/locales/en.yml

config/routes.rb

config/settings.yml

package.json

spec/controllers/tags_controller_spec.rb