### 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

{
public:
    CWallet * const pwallet;
    CTxDestination result;
    bool already_witness;
    explicit Witnessifier(CWallet *_pwallet) : pwallet(_pwallet), already_witness(false) {}
    bool operator()(const CKeyID &keyID) {
        if (pwallet) {
            CScript basescript = GetScriptForDestination(keyID);
            CScript witscript = GetScriptForWitness(basescript);
            SignatureData sigs;
            
            
            
            if (!ProduceSignature(DummySignatureCreator(pwallet), witscript, sigs) ||
                !VerifyScript(sigs.scriptSig, witscript, &sigs.scriptWitness, MANDATORY_SCRIPT_VERIFY_FLAGS | SCRIPT_VERIFY_WITNESS_PUBKEYTYPE, DummySignatureCreator(pwallet).Checker())) {
                return false;
            }
            return ExtractDestination(witscript, result);
        }
        return false;
    }
    bool operator()(const CScriptID &scriptID) {