Fix not-HAVE_SYMLINK code in zic.c.

I broke this in commit f3094920.  Apparently it's dead code anyway,
at least as far as our buildfarm is concerned (and the upstream IANA
code doesn't worry at all about symlink() not being present).
But as long as the rest of our code is willing to guard against not
having symlink(), this should too.  Noted while investigating a
tangentially-related complaint from Sandeep Thakkar.

Back-patch to keep branches in sync.