Update or remove the lode-linear example

[Luthaf]

https://atomistic-cookbook.org/examples/lode-linear/lode-linear.html

This example still uses equisolve, and should be updated to use code from metatensor-learn or removed.

Authors: @PicoCentauri @kvhuguenin

[PicoCentauri]

For me it is fine to remove it.