Storage sound is now controlled by var

Realized the previously removed MouseDrop override for pill bottles was
to stop the rustle sound from playing.
Cleaned up reference to outdated proc

Removed references to outdated get_equipped_items(). Still one left.
Removed unnecessary override for belts.
Backpacks now play sound when un/equipped

They did this before, but that was due to all storage items playing
sound. Now only applies to backpacks.