Change deleteat! to delete!

[dpsanders]

As far as I can tell, there is no overlap between the methods of deleteat! and those of delete!.
I suggest that deleteat! can simply become delete!.

[dpsanders]

Dup of #20531.

But it still really feels like deleteat! should just be delete!.

[andyferris]

I actually feel the opposite way here...

I'd like to see a coherent (across a range of different container types) interface for containers whose keys might change. With delete! a single key is removed. With deleteat! a key is removed and a whole string of other key-values are remapped. In this sense, they are different generic functions.

I've been tempted to open an issue about insert!. Dictionaries should probably support separate operations for insert, update, and so-called "upsert" (current behavior of Dict's setindex!). If deleteat! follows a different semantic to delete! then (to me) it might follow that insert! for Vector might be better called insertat! and support an insert-only insert! function for AbstractDicts.

[brenhinkeller]

Given the expanses of elapsed time and how breaking it would be nowadays, I'm tempted to call this "not planned", but feel free to undo!