Revert "world: avoid callbacks all over"

This reverts commit 75e669d.

Author: dbartolini

src/world/world.cpp

@@ -183,6 +183,10 @@ World::~World()
 		destroy_gui(*gui);
 	}
 
+	// Destroy units
+	for (u32 i = 0; i < array::size(_units); ++i)
+		_unit_manager->destroy(_units[i]);
+
 	// Destroy subsystems
 	CE_DELETE(*_allocator, _animation_state_machine);
 	CE_DELETE(*_allocator, _mesh_animation_player);
@@ -194,12 +198,6 @@ World::~World()
 	CE_DELETE(*_allocator, _scene_graph);
 	destroy_debug_line(*_lines);
 
-	// Destroy units.
-	for (u32 i = 0; i < array::size(_units); ++i) {
-		CE_ENSURE(_unit_manager->alive(_units[i]));
-		_unit_manager->destroy(_units[i]);
-	}
-
 	_marker = 0;
 }