Settings screen shows "Private Keys on device" even if the MSK is missing

[richvdh]

Suppose you have a device which (for historical reasons) has the private user-signing and self-signing keys, but not the private master key.

In that case, the "cross signing" tab in settings will look like this:

"Private Keys on device" is incorrect. The listed keys are the public keys.

[richvdh]

This then causes other problems when you try to verify against this device: we will happily accept the verification request, but that still leaves the other device in an "out of sync" state: element-hq/element-meta#2642.