Rev. on this commit: https://github.com/odoo/odoo/commit/02ec09cb1c3e2d7bc7968f40c18f2208d7f3f498 A consequence of the above commit is that @ mention were broken: the dropup menu with partner propositions was not displaying when the user typed the first characters to mention a user (e.g. by typing "[at]demo" in order to show the proposed mention "[at]Demo User" in a dropup menu). This commit fixes the issue by reverting the logic of how mentions are provided by the chat_manager, while removing some dead code. note: [at] = @