[FIX] website_slides: remove creation of quizz in reporting

Currently in the slide.question view it is possible to open a form
to create new questions for quizzes, but it is impossible to fill the form with
the required information to create a new question. So the create button has no purpose.
This as "slide_id" is required but can't be set in the form.
Now the option to add question from the reporting tab 'Quizzes'
is removed as the questions (with the answers) are added in the form from
slide.slide.

closes odoo/odoo#37117

Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>