refactor(docs): api: systems: remove seperate sites for parts described in others yet

docs/api/systems/gitlab/ticket-assignee.md

-# Gitlab-Ticket Assignee
-
-!!! todo
-    write usage api docs

docs/api/systems/gitlab/ticket-builder.md

-# Gitlab-Ticket-Builder
-
-!!! todo
-    write usage api docs

docs/api/systems/gitlab/ticket-system-builder.md

-# Gitlab-Ticketsystem-Builder
-
-!!! todo
-    write usage api docs

mkdocs.yml

@@ -28,10 +28,7 @@ nav:
         - GitLab:
           - Filter: 'api/systems/gitlab/filter.md'
           - Ticket: 'api/systems/gitlab/ticket.md'
-          - Ticket Assignee: 'api/systems/gitlab/ticket-assignee.md'
-          - Ticket Builder: 'api/systems/gitlab/ticket-builder.md'
           - Ticketsystem: 'api/systems/gitlab/ticket-system.md'
-          - Ticketsystem Builder: 'api/systems/gitlab/ticket-system-builder.md'
   - Developers Guide:
     - Index: 'developers-guide.md'