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_dynamicpaint.c

@@ -74,9 +74,7 @@ static void freeData(ModifierData *md)
   dynamicPaint_Modifier_free(pmd);
 }
 
-static void requiredDataMask(Object *UNUSED(ob),
-                             ModifierData *md,
-                             CustomData_MeshMasks *r_cddata_masks)
+static void requiredDataMask(ModifierData *md, CustomData_MeshMasks *r_cddata_masks)
 {
   DynamicPaintModifierData *pmd = (DynamicPaintModifierData *)md;