edit: Solution all the way at the end, skip to the direct link if you are thinking TLDR.
After receiving one to many e-mails from LinkedIn with the message that e-mail contact x had joined LinkedIn, I started looking for a way to delete these contacts or address book and stop receiving these mails. It turns out this is not as easy as you think.
Firstly disable the sending of these e-mails is not possible, it’s not listed on the options to opt-out of different kinds of e-mail communications from LinkedIn.
If you read some posts on the internet everyone keeps reffering to https://www.linkedin.com/contacts/manage_sources/ but this only lists options to add sources for synchronizing, I had nothing enabled so I couldn’t disable anything. At the top of content it showed me the number of LinkedIn connections and I could click on that, but it showed me a list of my connections, even after changing the filters to saved contacts it didn’t show anything besides connections.
So the wise thing to do is open a support ticket, and so I did but 5 days later the support person could only send me standard responses and did not really understand or read my question.
SOLUTION: I then finally found the answer by accident after I was changing my profile information.
When you get to this page: https://www.linkedin.com/fetch/importAndInviteEntry it show at the top Manage imported contacts. And that brings you to this page: https://www.linkedin.com/people/contacts where you will see all your imported contacts and you can delete them all.
Finally, no thanks to LinkedIn support.