This change removes an obsolete part of the Microsoft account integration that is no longer used after a previous update. It simplifies maintenance without changing how users connect or use Microsoft services in Odoo.

In this PR, after this merged PR  https://github.com/odoo/odoo/pull/204899 the `generate_refresh_token` not used anymore.

Old code for handling insufficient credit warnings in the IAP area has been removed because it was no longer used. This reduces maintenance overhead without changing the current user experience, since the active notification service already handles these cases.

The code to handle the insufficient credit errors isn't used in practice, it was replaced by the `iapNotification` service in `iap_mail` a long time ago.