Warning: ‘focus-out-hook’ is an obsolete variable

Hi there,

I wanted to log a warning that I am detecting with Emacs `28.0.50`:

```
Warning (comp): company-quickhelp.el:243:14: Warning: ‘focus-out-hook’ is an obsolete variable
```

I know it's probably early for a fix but here is a little reminder for myself or whoever gets first!

...and thanks for this package!
