Remove special case supply of land units from ships carrying them

Remove special case supply of land units from ships carrying them

The common supply code does not supply a land unit from the ship
carrying it, only resupply_all() does that, since 4.3.14.  It would be
nice to fix the inconsistency by always supplying land units that way,
but that's relatively costly now, because of the supply code's design.
Just drop it for now.

Affects load and lload (except resupply is disabled there because it's
buggy), supply, assault and board.