Following the iOS 11 move when Apple removed system-level integration with third party internet accounts like Facebook, Twitter, Flickr, and Vimeo, macOS Mojave will do the same thing.
Third Party Integration
Reddit user u/Marc1199 found that integration with Facebook, Twitter, and others are gone from macOS Mojave. You can find this by going to System Preferences > Internet Accounts.
This means that sharing options in the Notification Center, and also sharing things from other apps like Safari, will be gone. But this fits into Apple’s larger narrative of enhancing privacy.