Consider removing apply and lambda completely

[joelostblom]

Copied from slack:

What do you think of not teaching apply and lambda at all? It might sound radical at first, but I don't think we need to use these anywhere in dsci 100. The examples we have there right now are better done in other ways, and after spending the last hour trying to come up with better examples, I think all use cases where apply and lambda are justified are too advanced for dsci 100 (and honestly maybe also for MDS based on how I see students often use it). This would cut down the material and reduce complexity at seemingly no/little cost from what I can tell. I can make a PR of what this would look like in all the chapters (we rarely use them already so there would not be that many changes), unless you think it is too preposterous of a suggestion =)

Trevor mentioned this is not the most important thing to do right now so I will hold off with it.

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Edit: Also note that the way we suggest to use apply makes the syntax more complicated. E.g

region_lang.loc[:, "mother_tongue":"lang_known"].apply(lambda col: col.astype("int32"))

instead of just

region_lang.loc[:, "mother_tongue":"lang_known"].astype("int32")

and apply(max, axis=1 instead of .max(axis='index')