MMS "tap to download" and auto-retrieve settings is shown in secondary users despite them being nonfunctional

[inthewaves]

The Messaging app currently doesn't download MMS in secondary users, e.g. see the various comments in https://github.com/GrapheneOS/Messaging/blob/12/src/com/android/messaging/datamodel/data/MessageData.java#L593-L602

    public boolean canDownloadMessage() {
        if (OsUtil.isSecondaryUser()) {
            // Secondary users can't download mms's. Mms's are downloaded by bugle running as the
            // primary user.
            return false;
        }
        // Can download if status is retrying auto/manual downloading
        return (mStatus == BUGLE_STATUS_INCOMING_RETRYING_MANUAL_DOWNLOAD ||
                mStatus == BUGLE_STATUS_INCOMING_RETRYING_AUTO_DOWNLOAD);
    }

For the new rewrite, undownloaded MMS messages will say "Tap to download" which do nothing when in a secondary user

Also the auto-retrieve MMS setting is a no-op because secondary user Messaging app doesn't download MMS. It should probably just refer users to the main/owner user