Remove Yahoo login support from core and deprecate OpenID2.0 (#7310)

- Plugin developers using OpenID2.0 should migrate to OAuth2 or OIDC. OpenID2.0 APIs will be removed in v2.4.0

- For sites requiring Yahoo login, it can be implemented using the OpenID Connect plugin: https://meta.discourse.org/t/103632

For more information, see https://meta.discourse.org/t/113249

test/javascripts/helpers/site-settings.js

@@ -28,7 +28,6 @@ Discourse.SiteSettingsOriginal = {
   allow_new_registrations: true,
   enable_google_logins: true,
   enable_google_oauth2_logins: false,
-  enable_yahoo_logins: true,
   enable_twitter_logins: true,
   enable_facebook_logins: true,
   enable_github_logins: true,