Separate toasts for existing & new device verification

Separate device verification toasts into ones for devices that were
there when the app loaded and a separate toast for each device that
has appeared since.

Reverts part of https://github.com/matrix-org/matrix-react-sdk/pull/4506
(clicking a device from your own UserInfo now triggers the legacy
verification flow again).

Fixes https://github.com/vector-im/riot-web/issues/13422
Fixes https://github.com/vector-im/riot-web/issues/13418

src/SlashCommands.tsx

@@ -836,7 +836,7 @@ export const Commands = [
                     const fingerprint = matches[3];
 
                     return success((async () => {
-                        const device = await cli.getStoredDevice(userId, deviceId);
+                        const device = cli.getStoredDevice(userId, deviceId);
                         if (!device) {
                             throw new Error(_t('Unknown (user, session) pair:') + ` (${userId}, ${deviceId})`);
                         }