CLN: final Panel cleanup

[jreback]

I think we can take the final step an remove all remaining references to Panel.

(pandas) bash-3.2$ grep -r Panel pandas --exclude '*.pickle' --exclude *.msgpack --include '*.py' |wc
     146     911   11617

note that the pickle & msgpack files will stay.

TODO

• Have _constructor_expanddim raise a Notimplementederror

[jreback]

anything left on this

cc @pandas-dev/pandas-core

[datapythonista]

I opened #26627, I couldn't find anything else.

[jbrockmendel]

Were the pickle/msgpack files ever recreated without Panel?

[WillAyd]

@jbrockmendel is that all we need to do is basically re-save those test files?

[jbrockmendel]

is that all we need to do is basically re-save those test files?

Using the older pandas versions, yah. When I tried to do this a few months ago it didn't go great, don't remember off the top of my head what went wrong.

[jbrockmendel]

@WillAyd #25250

[simonjayhawkins]

there seems a small bit of panel specific code in to_xarray in core.generic.

it's not tested for self.ndim> 2, ok to remove?