[CentOS] what updates /etc/localtime?

I see in CentOS 7 that /etc/localtime is a symlink (which seems
sensible...) but in earlier versions it is a copy of some file from
under /usr/share/zoneinfo.
rpm -q --scripts tzdata
does not show any postinstall script, so in the non-symlink versions,
how does the copied /etc/localtime file get updated with new zone
data?

-- 
   Les Mikesell
      lesmikesell at gmail.com