Punt iputils_common helpers.

Punt iputils_common helpers.

Only two functions from this common library are used by rarpd.

The error fallback depends on program_invocation_short_name, which is a
GNU C library feature, and if you have the GNU C library, you have error,
so I'm really not sure what systems this works on.

And for rarpd, there seems to be no point in explicitly closing the
standard I/O streams since it doesn't print anything normally.