Remove reference to Mozilla VPN on about:privatebrowsing

[2br-2b]

Going to about;privatebrowsing on a non-private window shows the following:

This should be changed from Mozilla VPN to advertise Ghostery's products. Where should it link to? Ghostery Midnight, Ghostery Premium, or somewhere else?

I would say Ghostery Midnight, but since that isn't compatible with Linux, we'd need a different link for Linux users, and it's probably easier to just have one link rather than needing a different one for each OS.