I got an update from support:
"It is my understanding that you'd like to remove all the notes listed from the "Shared with me" section.
I would like to set the right expectation that the Shared with Me tab only acts as a history of all notes that have been shared with you, regardless if you still have access to them or the owner has stopped sharing those notes. At the moment, it's a "view" and not a manageable list. We're in the process of fixing and redesigning sharing, and this view will likely be changed/improved. Please know that the behavior above is the current behavior for the near future.
I’ve gone ahead and made note of this for our development team. While we can’t commit to getting all feature requests into the product, we do rely on our community to tell us what they’d like to see in the future.
Thank you for your time to contact us. Let me know if you have any other questions, and enjoy the rest of your week!"