Hide table of contents on notebooks page

[jackgerrits]

Why are these changes needed?

The table of contents is empty on this page and it makes the layout look strange.

Related issue number

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://microsoft.github.io/autogen/docs/Contribute#documentation to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (9eab2b5) 35.28% compared to head (c0664b0) 35.28%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1600   +/-   ##
=======================================
  Coverage   35.28%   35.28%           
=======================================
  Files          44       44           
  Lines        5331     5331           
  Branches     1236     1236           
=======================================
  Hits         1881     1881           
  Misses       3296     3296           
  Partials      154      154           

Flag	Coverage Δ
unittests	35.28% <ø> (ø)

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