Remove unused items from RAWs. (Oktane, refined warp flasks, down)

Gone are the following, which were not used or createable anywhere:

    * Oktane juice
    * Refined warpstone flasks

Also gone is turning feathers into 'down'. Down beds already use feathers
directly, so creating down was a dead-end.

Commented-out magma and water bottles in item_z_orcfort have also been
removed; these are now permanently part of the main masterwork files.