Removed dup references to mass mailing lists
requested to merge odoo12-somconnexio-subpacketing-mass-mailing-fix-cooperator-api into odoo12-somconnexio-subpacketing
CHANGELOG:
### XXX
- [#nn](https://git.coopdevs.org/coopdevs/som-connexio/odoo-somconnexio/-/merge_requests/nn) Example text
Related card: https://trello.com/c/XXXXXXXX/xjksdjflsdfksldfsdfs