[FIX] portal: fix portal title for the salesperson data

Before this commit, if the helpdesk module was installed, the title of
the salesperson data was changed from "Your contact" to "Salesperson"
for portal users. This did not add any value and the title of the tab
also became "Salesperson" which we do not want. This commit allows to
keep the title "Your contact" above the salesperson information and to
not change the tab title.

Steps to reproduce the problem fixed by this commit:
- Run Odoo enterprise with helpdesk and sales installed.
- As the admin, create a helpdesk ticket with Joel Willis (portal user)
as the customer and save.
- Click on Joel Willis, select the "Sales & Purchases" tab and set a
salesperson.

=> Log in as Joel Willis and on /my, you will have "Salesperson" as the
title of the tab. This bad behavior is due to [this commit] that added a
title above the salesperson information. But with this change the title
of the tab was also impacted. Then [this other commit] added a default
title above the salesperson information. We can be satisfied with this
default title which does not alter the title of the tab.

[this commit]: https://github.com/odoo/enterprise/commit/700e9dec4a5c9fca354e063d6a85b0514832c84c
[this other commit]: https://github.com/odoo/odoo/commit/d5c66ca1fa5d0f364241636bd502342c1d4ee9ac



opw-3103718

closes odoo/odoo#108705

Related: odoo/enterprise#35240
Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>