Cleanup: Remove unused argument from modifier data mask callback

This isn't likely to be helpful in the future with the move to generic
attributes

source/blender/modifiers/intern/MOD_hook.c

@@ -68,9 +68,7 @@ static void copyData(const ModifierData *md, ModifierData *target, const int fla
   thmd->indexar = MEM_dupallocN(hmd->indexar);
 }
 
-static void requiredDataMask(Object *UNUSED(ob),
-                             ModifierData *md,
-                             CustomData_MeshMasks *r_cddata_masks)
+static void requiredDataMask(ModifierData *md, CustomData_MeshMasks *r_cddata_masks)
 {
   HookModifierData *hmd = (HookModifierData *)md;