Fix bad function definitions in Debian plugin

There appears to be a definition issue for some functions/aliases which
result in the following errors when sourcing .zshrc:

```
/home/username/.oh-my-zsh/plugins/debian/debian.plugin.zsh:75: defining function based on alias `abd'
/home/username/.oh-my-zsh/plugins/debian/debian.plugin.zsh:75: parse error near `()'
```

Fixes #7986