### 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

"2. \"newpassphrase\"      (string) The new passphrase\n"
            "\nExamples:\n"
            + HelpExampleCli("walletpassphrasechange", "\"old one\" \"new one\"")
            + HelpExampleRpc("walletpassphrasechange", "\"old one\", \"new one\"")
        );
    }
    LOCK2(cs_main, pwallet->cs_wallet);
    if (request.fHelp)
        return true;
    if (!pwallet->IsCrypted()) {
        throw JSONRPCError(RPC_WALLET_WRONG_ENC_STATE, "Error: running with an unencrypted wallet, but walletpassphrasechange was called.");
    }
    
    
    SecureString strOldWalletPass;
    strOldWalletPass.reserve(100);
    strOldWalletPass = request.params[0].get_str().c_str();
    SecureString strNewWalletPass;
    strNewWalletPass.reserve(100);
    strNewWalletPass = request.params[1].get_str().c_str();
    if (strOldWalletPass.length() < 1 || strNewWalletPass.length() < 1)
        throw std::runtime_error(
            "walletpassphrasechange <oldpassphrase> <newpassphrase>\n"
            "Changes the wallet passphrase from <oldpassphrase> to <newpassphrase>.");
    if (!pwallet->ChangeWalletPassphrase(strOldWalletPass, strNewWalletPass)) {
        throw JSONRPCError(RPC_WALLET_PASSPHRASE_INCORRECT, "Error: The wallet passphrase entered was incorrect.");
    }
    return NullUniValue;
}
UniValue walletlock(const JSONRPCRequest& request)