How do I delete/remove a shell function?
In Zsh:
unfunction zThat's another (arguably better) name for unhash -f z or unset -f z and is consistent with the rest of the family of:
unsetunhashunaliasunlimitunsetopt
When in doubt with such things, type un<tab> to see the complete list.
(Slightly related: It's also nice to have functions/aliases like realiases, refunctions, resetopts, reenv, etc to "re-source" respective files, if you've separated/grouped them as such.)