fix: Stop using view_auth_classes helper in discussions API
fix: Stop using view_auth_classes helper in discussions API

as it conflicts with the manually-assigned `permission_classes`;
the decorator erases them.

EDUlib/edx-platform,EDUlib/edx-platform,arbrandes/edx-platform,EDUlib/edx-platform,EDUlib/edx-platform,angelapper/edx-platform,arbrandes/edx-platform,edx/edx-platform,angelapper/edx-platform,angelapper/edx-platform,eduNEXT/edx-platform,eduNEXT/edx-platform,arbrandes/edx-platform,edx/edx-platform,edx/edx-platform,edx/edx-platform,arbrandes/edx-platform,eduNEXT/edx-platform,angelapper/edx-platform,eduNEXT/edx-platform