Followup on 5ce8f1e375
Before this commit, There would be traceback on Launching Plan with `Responsible` set to `other` and No `Responsible Person` defined on activity due to Extra argument.
In this commit, We remove that extra Argument.
closes odoo/odoo#44965
X-original-commit: 009e5526ee398415693d1d3df8f3c2ac546fd258
Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>