[REV] web: deletion of lines in export profiles

This reverts commit 814fb43e.

After #129567 the lines in export profiles which correspond to field
relations attributes get deleted whenever you access to them in the
export profile. This is leading to a huge lost of users custom data.

Closes #134791

closes odoo/odoo#134949

Signed-off-by: Julien Castiaux (juc) <juc@odoo.com>