Also say "Connect ..." on remaining key backup buttons
This updates the remaining buttons shown when a backup exists but is not trusted
so that they all now say "Connect this device to Key Backup" instead of "Use Key
Backup".
This is a follow up to https://github.com/matrix-org/matrix-react-sdk/pull/2917
and was agreed with Riot iOS team
https://github.com/vector-im/riot-ios/pull/2375#issuecomment-485788118.
Fixes https://github.com/vector-im/riot-web/issues/9542
