Remove some unnecessary variable exports

roles/display_manager/tasks/main.yml

@@ -2,4 +2,3 @@
 - name: Include display manager strategy.
   include_role:
     name: "display_manager/{{ display_manager }}"
-    public: true

roles/display_server/tasks/main.yml

@@ -2,4 +2,3 @@
 - name: Include display server strategy.
   include_role:
     name: "display_server/{{ display_server }}"
-    public: true

roles/window_manager/tasks/main.yml

@@ -2,4 +2,3 @@
 - name: Include window manager strategy.
   include_role:
     name: "window_manager/{{ window_manager }}"
-    public: true