🐛 delta zsh completion was overrided by zsh builtin completion

delta has its zsh completion
<https://github.com/dandavison/delta/blob/master/etc/completion/completion.zsh>,
however it cannot work, because
</usr/share/zsh/functions/Completion/Unix/_sccs> will override it.

```
❯ rg delta ~/.zcompdump
296:'delta' '_sccs'
❯ delta -<Tab>
option
-s   silent
-y   specify delta commentary
```

Any method to avoid this conflict? Thanks!