DOC: Remove shared axis examples

As proposed in matplotlib#24958 (comment)

> I think these two examples should both be deleted as they use a clunky
 incremental subplot() creation, which IMHO is not great for generating
 > multiple subplots, in particular if you go into more complex logic
 like sharing.

In addition, sharing is extensively handled in https://matplotlib
.org/stable/gallery/subplots_axes_and_figures/subplots_demo.html#sharing-axes

Author: timhoffm