Update textbook.en.md

00.brainstorming-pedagogical-teams/45.synthesis-structuring/10.math-tools/20.n2/textbook.en.md

@@ -3,11 +3,6 @@ title: Brainstorming on the mathematical tools required at each level
 published: true
 routable: true
 visible: false
-lessons:
-    - slug: brainstorming-123-mathematical-tools
-      order: 2
-    - slug: brainstorming-234-mathematical-tools
-      order: 1
 ---
 
 #### Brainstorming on the mathematical tools required at level 2