There may be some confusion about what Delve is. Delve tries to figure out what documents are important to you (the viewing user) and displays them to you. This means that what you see in Delve will be different from what others see. It also respects permissions on files. From Are my documents safe in Office Delve?:
Delve never changes any permissions. Only you can see your private
documents in Delve.
Also, other people can't see your private activities, such as what
documents you've read, what emails you've sent and received, or what
Skype for Business conversations you've been in. Other people can see
that you've modified a document, but only if they have access to the
What you see in Delve is different from what other people see. You can
see your private documents and other documents that you have access
to. Other people can see their documents and documents that they have
While you might be able to hide documents from the Delve view, they are still accessible to you either through group membership or explicit sharing.
To completely remove them would require that you disallow all sharing from a user's OneDrive for Business site and revoke any currently shared documents. If you have sharing concerns, you might want to consider disabling external sharing or limit sharing to specific domains.