Purpose of this commit is to remove code coming from old features,
implementations and that was not completely cleaned.
Including
* remove support of old "reply" composition mode which is simply a comment
with a parent message, and is deprecated;
* remove support of old "mail.compose.message.mode" context key that was
used in Odoo 6.1;
* remove support of message_id default value in context instead of
default_parent_id;
* remove old redirection of user / partner post. This code come from
old age when people were able to post on their "profile" by posting
on their user;
* remove unnecessary method for selection field;
* remove unused imports to clean a bit code;
We also make some optional parameters in rendering methods mandatory to
ease code understanding and future modifications.
Task ID 1853147
PR #39272
Thibault Delavallée
7ec2e85734