Remove links to deleted notebooks (#120)

The links to deleted notebooks in `learn.md` now have been removed.
Related to pybamm-team/PyBaMM#3750

content/learn.md

@@ -29,8 +29,6 @@ If you would like to get started with PyBaMM, you may go through the [Getting St
 - [Tutorial 7: Model options](https://colab.research.google.com/github/pybamm-team/PyBaMM/blob/main/docs/source/examples/notebooks/getting_started/tutorial-7-model-options.ipynb)
 - [Tutorial 8: Solver options](https://colab.research.google.com/github/pybamm-team/PyBaMM/blob/main/docs/source/examples/notebooks/getting_started/tutorial-8-solver-options.ipynb)
 - [Tutorial 9: Changing the mesh](https://colab.research.google.com/github/pybamm-team/PyBaMM/blob/main/docs/source/examples/notebooks/getting_started/tutorial-9-changing-the-mesh.ipynb)
-- [Tutorial 10: Creating a model](https://colab.research.google.com/github/pybamm-team/PyBaMM/blob/main/docs/source/examples/notebooks/getting_started/tutorial-10-creating-a-model.ipynb)
-- [Tutorial 11: Creating a submodel](https://colab.research.google.com/github/pybamm-team/PyBaMM/blob/main/docs/source/examples/notebooks/getting_started/tutorial-11-creating-a-submodel.ipynb)
 
 For more resources, please refer to the [Examples section](https://docs.pybamm.org/en/stable/source/examples/index.html) in the PyBaMM documentation.