RFC, MAINT: use pooch for download management?

[drammock]

Describe the new feature or enhancement

Scikit-image recently switched to using pooch for dataset download management. Let's see if it works well enough that we could eliminate our dataset downloading code. WDYT?

[larsoner]

+1 for me. See also some discussion in sphinx-gallery/sample-project#3

[adam2392]

FYI this is now closed by #9742