Stop quarry duplicating items

The quarry was digging via dig_node and also manually putting the node's
drops into the tube system.  This assumed that dig_node would attempt
to put the drops in the player's inventory, doing nothing if there is
no such inventory.  With the item_drop mod installed, dig_node would
instead turn the node into an item entity, so the quarry's strategy would
duplicate the item, making it appear both as an item entity in situ and
as an item in the tube.  Instead, the quarry must use remove_node when
it manually processes the drops, just like the pipeworks node breaker.