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_explode.c

@@ -76,9 +76,7 @@ static bool dependsOnTime(struct Scene *UNUSED(scene), ModifierData *UNUSED(md))
 {
   return true;
 }
-static void requiredDataMask(Object *UNUSED(ob),
-                             ModifierData *md,
-                             CustomData_MeshMasks *r_cddata_masks)
+static void requiredDataMask(ModifierData *md, CustomData_MeshMasks *r_cddata_masks)
 {
   ExplodeModifierData *emd = (ExplodeModifierData *)md;