### Describe the issue

I added a second new wallet2.dat. Now I wanted to encrypt it, but `bitcoin-cli help` does not show the command to do so, I need to use `bitcoin-cli -rpcwallet=wallet2.dat help`. This is very un-intuitive, and bad for a help function.

### Can you reliably reproduce the issue?

1. have an encrypted default wallet
2. add new multi wallet wallet2.dat via config file or cmd line options
3. naive `bitcoin-cli help` does not show command to encrypt second wallet.

### Expected behaviour

All wallet encryption, lock and unlock commands should be shown unconditionally in `bitcoin-cli help`.

The dynamic hiding of some lines is arguably worse than the benefit with multiple wallets.

### Actual behaviour

`bitcoin-cli help` shows only wallet encryption commands appropriate for the default wallet.

### What version of bitcoin-core are you using?

bitcoind 0.15.0.1~dfsg-1
deb http://ppa.launchpad.net/luke-jr/bitcoin-core-bip148-unofficial-builds/ubuntu zesty main

### Machine specs:
- OS: Debian 9.2

{
    CWallet * const pwallet = GetWalletForJSONRPCRequest(request);
    if (!EnsureWalletIsAvailable(pwallet, request.fHelp)) {
        return NullUniValue;
    }
    if (request.fHelp || request.params.size() < 1 || request.params.size() > 2)
    {
        std::string msg = "addwitnessaddress \"address\" ( p2sh )\n"
            "\nAdd a witness address for a script (with pubkey or redeemscript known).\n"
            "It returns the witness script.\n"
            "\nArguments:\n"
            "1. \"address\"       (string, required) An address known to the wallet\n"
            "2. p2sh            (bool, optional, default=true) Embed inside P2SH\n"
            "\nResult:\n"
            "\"witnessaddress\",  (string) The value of the new address (P2SH or BIP173).\n"
            "}\n"
        ;
        throw std::runtime_error(msg);
    }
    {
        LOCK(cs_main);
        if (!IsWitnessEnabled(chainActive.Tip(), Params().GetConsensus()) && !gArgs.GetBoolArg("-walletprematurewitness", false)) {
            throw JSONRPCError(RPC_WALLET_ERROR, "Segregated witness not enabled on network");
        }
    }
    CTxDestination dest = DecodeDestination(request.params[0].get_str());
    if (!IsValidDestination(dest)) {
        throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Invalid Bitcoin address");
    }