Revert "Use `VISIBILITY_UNKNOWN` as condition"
Revert "Use `VISIBILITY_UNKNOWN` as condition"

This reverts commit 0122d73e0ee21a848625fda132f6077dcd864c1f.

The right condition is to filter whether the user is visible (contact)
or not. It's not enough to send the email when the visibility is
unknown, since a user that was once a contact is kept as hidden, so the
userhandle is known (same problem we're trying to solve).

meganz/sdk,meganz/sdk,Acidburn0zzz/sdk,meganz/sdk,Acidburn0zzz/sdk,Acidburn0zzz/sdk,Acidburn0zzz/sdk,meganz/sdk,Acidburn0zzz/sdk,meganz/sdk,Acidburn0zzz/sdk,meganz/sdk,meganz/sdk,Acidburn0zzz/sdk,Acidburn0zzz/sdk