When the wallet is rescanned at startup in `bitcoind`, there seems to be no way to interrupt that in a clean way (other than forcefully killing the process).
{
    LOCK(cs_wallet);
    std::set<CTxDestination> result;
    for (const std::pair<CTxDestination, CAddressBookData>& item : mapAddressBook)
    {
        const CTxDestination& address = item.first;
        const std::string& strName = item.second.name;
        if (strName == label)
            result.insert(address);
    }
    return result;
}
void CWallet::DeleteLabel(const std::string& label)