Purpose of this commit is to clean field definitions by
* doing compute in batch: especially when the loop can be reduced to a single
computation / batch assignment (based on groups or config parameter for
example);
* remove default when having a compute as computes should completely define
the field value at any time;
Some side dish code cleaning is performed at the same time: unnecessary
import or dead code removal.
Task-2638444
PR odoo/odoo#76005
Co-Authored-By: Thibault Delavallée <tde@odoo.com>
Co-Authored-By: Victor Feyens <vfe@odoo.com>