Remove legacy project routes

What does this MR do and why?

We introduced subgroups in version 9 which meant our wildcard namespaced routes were unable to guarantee a match to the project name if project is in a subgroup. As part of an ongoing effort in #28848 (closed) we have been deprecating unscoped routes and redirecting to the /-/ scoped routes. In 16.0 we are removing the redirected routes.