[IMP] project, website_slides(_forum): no need to forward debug in URL

Now that the debug mode is stored in session (see parent commit), there is no
need anymore to forward the debug query param.

This commit clean the occurence of code that were doing that by using mainly
`keep_query`.

task-1934445
Comes with https://github.com/odoo/enterprise/pull/4281
Closes #33213