inventory_selector: clean up deprecated code

[andrei8l]

Summary

None

Purpose of change

There's a lot of confusing, deprecated code in inventory_ui.
Items gets stacked and moved around for no good reason several times.
Items in a trader's inventory gets sorted under "Items Worn" instead of categorizing correctly (the bug I was trying to fix!)

Describe the solution

Spank deprecated and/or duplicated code.
Put the items in the right columns/categories instead of moving them with toggle_categorize_contained() after building the list.

Describe alternatives you've considered

N/A

Testing

Every UI based on inventory_selector (inventory, eat, multidrop, unload, activate, pickup, compare, etc) should look and function exactly the same as before with these 3 changes:

• items in magazine{s, wells} aren't shown anymore (batteries, pen ink, etc)
• all trader items are categorized correctly in the trade UI. Items stashed in worn/wielded containers aren't listed under "Items Worn" anymore
• contents in the same category as their container get sorted under their container even when the column is forced to not indent

Additional context

N/A

[andrei8l]

Thanks for merging.