[FIX] mail: correct mistakes introduced with new environment

Some mistakes slipped into the PR introducing the new environment in the discuss
app. This PR fixes those mistakes :

- triggers on this.env.bus that were listen on core.bus
- inconsistent service names between discuss_public_boot/main
- call to Component.env.services.messaging while messaging was available in this.env
- remaining useSubEnv in container that were not needed anymore

closes odoo/odoo#92533

Signed-off-by: Sébastien Theys (seb) <seb@odoo.com>

addons/knowledge/static/src/components/permission_panel/permission_panel.js

@@ -253,7 +253,7 @@ class PermissionPanel extends Component {
             const userId = userIds && userIds.length === 1 ? userIds[0] : false;
 
             if (userId) {
-                const messaging = await Component.env.services.messaging.get();
+                const messaging = await this.env.services.messaging.get();
                 messaging.openChat({
                     userId: userId
                 });