Cleanup: use proper ObjectWalkFunc typedef in modifiers' object callback func.

Also, fix own stupidity, no need to define ID callback in case we only have objects,
calling code knows to fallback to `foreachObjectLink()` when `foreachIDLink()` is missing...

source/blender/modifiers/intern/MOD_armature.c

@@ -91,8 +91,7 @@ static bool isDisabled(ModifierData *md, int UNUSED(useRenderParams))
 
 static void foreachObjectLink(
         ModifierData *md, Object *ob,
-        void (*walk)(void *userData, Object *ob, Object **obpoin),
-        void *userData)
+        ObjectWalkFunc walk, void *userData)
 {
 	ArmatureModifierData *amd = (ArmatureModifierData *) md;