[FIX] mail: delete messages on module uninstallation
[FIX] mail: delete messages on module uninstallation

When uninstalling a module, the messages linked to the records
of that module are not deleted leading to ghost messages when
reinstalling the module.

This is due to the lack of foreign keys in the definition of the
chatter making it impossible to cascade delete.

opw-1928208

closes odoo/odoo#30798
ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo