Now that OOUI's "alerts" icon pack includes all the icons we need, we can use it and get rid of the badgeicons module.
- Replace uses of the ext.echo.badgeicons module with oojs-ui.styles.icons-alerts
- Delete the ext.echo.badgeicons module definition in extension.json
- Delete modules/icons/badgeicons.json and the icon files it refers to (badge.svg and tray.svg)
Requires
- Apex to feature 'alerts' icon pack as well – https://gerrit.wikimedia.org/r/#/c/298031/
- T145163: Slim down the "alerts" icon pack to the bare essentials
- Upstream 'double-check' icon to OOUI 'interactions' pack; added in 786c7e180fc0e4542a41cc0ae1e4c2961516aefb