### 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

}
    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 walletpassphrase was called.");
    }
    
    SecureString strWalletPass;
    strWalletPass.reserve(100);
    
    
    strWalletPass = request.params[0].get_str().c_str();
    if (strWalletPass.length() > 0)
    {
        if (!pwallet->Unlock(strWalletPass)) {
            throw JSONRPCError(RPC_WALLET_PASSPHRASE_INCORRECT, "Error: The wallet passphrase entered was incorrect.");
        }
    }
    else
        throw std::runtime_error(
            "walletpassphrase <passphrase> <timeout>\n"
            "Stores the wallet decryption key in memory for <timeout> seconds.");
    pwallet->TopUpKeyPool();
    int64_t nSleepTime = request.params[1].get_int64();
    pwallet->nRelockTime = GetTime() + nSleepTime;
    RPCRunLater(strprintf("lockwallet(%s)", pwallet->GetName()), boost::bind(LockWallet, pwallet), nSleepTime);
    return NullUniValue;
}
UniValue walletpassphrasechange(const JSONRPCRequest& request)