libevent seems to have invaded `libbitcoin_common` via `url.cpp`

`url.cpp` is used only from `test/fuzz/string.cpp` and `wallet/rpcwallet.cpp`

libevent should only be required for bitcoind, bitcoin-cli and (due only to the hack of passing wallet names) bitcoin-qt

public:
    UniValue PrepareRequest(const std::string& method, const std::vector<std::string>& args) override
    {
        UniValue params;
        if(gArgs.GetBoolArg("-named", DEFAULT_NAMED)) {
            params = RPCConvertNamedValues(method, args);
        } else {
            params = RPCConvertValues(method, args);
        }
        return JSONRPCRequestObj(method, params, 1);
    }
    UniValue ProcessReply(const UniValue &reply) override