Eliminate use of __attribute__

Ideally this would be standard C++, but here I've settled for things that should be supported by both clang and VS/cl.exe:
- Deprecated attribute retained, but now uses __declspec syntax
- Packed attribute replaced with pragma pack, except one instance where it unnecessary
- Aligned attribute replaced with explicit padding bytes inserted in the structs where needed
- Unused attribute simply removed (though where possible, the unused entities were also removed)

osx/scenedit/scen.core.h

@@ -1,5 +1,5 @@
 
-void init_scenario() __attribute__((deprecated));
+__declspec(deprecated) void init_scenario();
 short edit_ter_type(ter_num_t which_ter);
 short edit_monst_type(short which_monst);
 cMonster edit_monst_abil(cMonster starting_record,short parent_num);