[Doc]: mpl_toolkits.axes_grid still mentioned as maintained

[oscargus]

Documentation Link

https://matplotlib.org/stable/api/toolkits/axes_grid.html?highlight=axes_grid

Problem

As far as I can tell, it is completely removed.

Suggested improvement

Change the wording to say something correct. Possibly when it was removed.

[oscargus]

I realize now that this is solved by import magic.

[oscargus]

Oh, and I also realize that this was actually removed in #22886 but that https://github.com/matplotlib/matplotlib/blob/main/doc/api/toolkits/axes_grid.rst wasn't removed or edited.

Not sure what the best thing is to do here. Remove and redirect to axes_grid1 (possibly with a note that some functionality is in axisartist)?

Marked as Release critical since this is a major inconsistency in the docs.

[tacaswell]

not a blocker for rc2