feat: remove waffle flags for managing course outline sidebar (#1713)

* feat: remove waffle flags for managing course outline sidebar

* fix: flag and tests

* fix: product-tours tests

* fix: remove default content for SequenceNavigationSlot and update tests

* fix: remove default content for CourseBreadcrumbsSlot

* fix: update plugin-slots version and documentation

* revert: update plugin-slots version

* fix: update tests