Remove option LANDSPIES, customize table land-chr instead

Remove option LANDSPIES, customize table land-chr instead

Spy units are now enabled when a land unit type with capability spy
exists.  To disable them, deities have to customize table land-chr.

Before, spy units types were ignored when option LANDSPIES was
disabled.  Except for xdump land-chr, which happily dumped unusable
spy unit types.