This commit removes a lot of legacy code that we kept for the few legacy client actions that were still to be converted to owl. Now that the last one has been converted, we can finally get rid of a lot of legacy code (ActionAdapter, ActionMixin, ControlPanel, ActionMenus, DropdownMenu(Item), Pager, DomainSelector...). Part of task~3439226 closes odoo/odoo#129314 Related: odoo/enterprise#44465 Signed-off-by: Aaron Bohy (aab) <aab@odoo.com>