load lload: Drop dead "cannot carry land units" checks

load lload: Drop dead "cannot carry land units" checks

load_land_ship() and load_land_land() fail for carriers that can't
carry any land units before prompting for land units to load.  They
then iterate over land units to load, and fail when the carrrier has
no room.  They either report "cannot carry land units" or "doesn't
have room for any more land units" then.  The former cannot happen.
Crept into load_land_ship() in Empire 2, blindly copied to
load_land_land() in 4.0.0.  load_plane_ship() and load_plane_land()
don't have this issue.

Drop the dead code.

Signed-off-by: Markus Armbruster <armbru@pond.sub.org>