If required, it is possible to customize the Share header menu bar, and hide
the Repository link. This means users will only be able to browse
content in document libraries of sites that they own, or are a member
of.
This blog post shows how to remove items from the Share header: Customizing the Share Header (Part 3). More generally
there is a tutorial on customizing the Share header that can be worked through in this
documentation: Customizing
Share Header Menu.