I'm not entirely sure what you're asking here, but I'll take a shot.
In general, we don't delete questions that have been marked as a duplicate because they serve as signposts to the answer - this is especially important for search results, as the duplicate might use different keywords and therefore show up in a wider range of searches. Deleting the duplicate would lose that ability. This also applies to migrated questions that have been moved from one site to another, as they also serve as a record of what happened to the post - the migration "stub" will be automatically removed after a period of time when it's deemed to have run its course of usefulness.
With that in mind:
1. Delete "Delete duplicate questions"
That link goes to this post on the main Open Source site, where you originally posted it. It has since been migrated to here - the question I'm answering. The link here goes to the migration stub, which we don't generally delete for the reasons above.
2. Delete "How license OpenSource Software?"
This question has been marked as a duplicate. Again, those aren't generally deleted for the reasons above.
3. Delete the highlighted part of "Practical steps to licence Free software and Open Source Projects"
I'm not sure what you mean by highlighted here. If you mean the part of the page with a red background, that red background means the post has been deleted - so, if that's your meaning, no further action is necessary here since it's already been deleted.
deletelink below the question body. (You can that for both How license OpenSource Software? and this question itself, if that's what you wanted to do.) For item #3, the red-colored posted are deleted; only you can see them.