Hi chameau and welcome. I hope you enjoy staying here
Let my try to help you.
> 1. Wonder how I can remove the Shortcut again in case I got fed up with it?
Just click in this shortcut field and press one of the following key: Shift or Ctrl or Alt
Now the shortcut field is empty and no shortcut is assigned anymore if you confirm by pressing the [OK] button.
> 2. Using the shortcut the .chm file shows up twice ...!
Yes, i can confirm this too,.... if we use Strg+F1 the CHM file opens twice