Deletion of single shared note is not possible

[korelstar]

Steps to reproduce:

• $USER1 shares a single file to $USER2
• $USER2 moves that shared file to the folder /Notes/
• $USER2 opens the notes app which lists the shared note
• When clicking the delete button for that note, a "NotPermittedException" is thrown.

Fix: Instead of deleting the file, the app should "unshare" the file, like it's done in the files app.

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[jancborchardt]

@nextcloud/sharing could you help here with debugging or a fix? :)