[FIX] board: do not display the no_content_create div
[FIX] board: do not display the no_content_create div

That div has been given an absolute position, which does not work inside another
div on the dashboard.
If there are other dashboard elements below, there are unusable since they are
covered by the no_content_create div.
Moreover, there is no create button on the dashboard, so we shouldn't even see
it.
It also spares us from seeing that hideous clippy-inspired smiling paper sheet.

opw 1907650

closes odoo/odoo#29076
ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo