The customizable "out of office" text was removed from the editable views as
part of task-2053585, but some places in the code were still using it, even
though it was never set anymore.
This commit removes the obsolete code.
Part of task-2171864
closesodoo/odoo#44968
Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>