Revert "Add version headers to submap buffer and overmaps. Bump version to 5 for 0.8"

This reverts commit fac3f16f29406e42e6559ce63a2fc5f5c886f9f5.
Split off code for loading old formats into game::unserialize_legacy, located in savegame_legacy.cpp
overmap: split open into open/unserialize/unserialize_legacy
mapbuffer: add load_legacy
Remove test
cleanup
mapbuffer: versioning and support for attempting an alternate loader. Split load into load and serialize
versioning and support for attempting an alternate loader. Split load into load and unserialize
savegame_legacy: initial stub functions for deprecated format loaders
extra save/load helper functions
item jsonsave/load: contents, syntax adjust
monster: save/ load inventory, additional json_load(data, game) method to
match item/player/npc
inventory: json save/load items, invcache
player, npc, skill, npc_* and pldata structs/classes: json_save, json_load.
Declared in class files, defined in savegame_json.cpp for easier tracking
Temporary #defines for testing which controls what is jsonized on save
editmap: hitting 'm' over monster or npc, or selecting savetest in edit item will pull up a
json dumper / reloader / editor / tester
Catamobile(tm): Built JSON though. (jsonized save/load)
editmap: cleanup, vehicle edit, item adding
Fixed typo causing 'p' segv
player::json_load: carp about non-existent bionics.id and discard.
Temporary comment