[IMP] mail: remove useless menu cache invalidation
[IMP] mail: remove useless menu cache invalidation

Rev. 15174e9a70b07f95356bf0a75887e2a02b33baab explicitly
cached ir.ui.menu entries, and required an explicit
cache invalidation when users changed their mail.group
subscriptions (mail.group used to override the ir.ui.menu
search(), cfr e.g. 89e404301bdaa57dc2bbe351bfefac993ade9b38)

The menu search() override is gone as of 9.0, so it's time we get
rid of the unnecessary cache invalidation.

hip-odoo/odoo,hip-odoo/odoo,dfang/odoo,ygol/odoo,ygol/odoo,hip-odoo/odoo,hip-odoo/odoo,dfang/odoo,dfang/odoo,hip-odoo/odoo,dfang/odoo,dfang/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,dfang/odoo,hip-odoo/odoo