iflib(9): Revert ancillary changes

In main, 7ff9ae90f reverted 09f6ff4f, i. e. support for cloning pseudo
interfaces along with "ancillary changes" part of the original commit.
As these latter were never actually used, this change turns the macros
into spares in stable/13, too. Thus, when the bits gets reused in main
such commits can be merged without conflicts.