I am pretty sure those functions are contained in zsh-5.5:
% rpm -lq zsh | grep -E 'compinit|compdef|is-at-least|add-zsh-hook' /usr/share/zsh/5.5/functions/_add-zsh-hook /usr/share/zsh/5.5/functions/_compdef /usr/share/zsh/5.5/functions/add-zsh-hook /usr/share/zsh/5.5/functions/bashcompinit /usr/share/zsh/5.5/functions/compinit /usr/share/zsh/5.5/functions/is-at-least
Did you (re)exec zsh in your already running sessions?
In a login session, you need to do something like this:
% exec zsh -l
This was discussed at https://bugzilla.redhat.com/1296692 where we agreed to not rebase zsh in stable Fedora releases to avoid troubles like this. However, f28 is not stable yet, so this is acceptable IMO.