### 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)
        throw std::runtime_error(
            "lockunspent unlock ([{\"txid\":\"txid\",\"vout\":n},...])\n"
            "\nUpdates list of temporarily unspendable outputs.\n"
            "Temporarily lock (unlock=false) or unlock (unlock=true) specified transaction outputs.\n"
            "If no transaction outputs are specified when unlocking then all current locked transaction outputs are unlocked.\n"
            "A locked transaction output will not be chosen by automatic coin selection, when spending bitcoins.\n"
            "Locks are stored in memory only. Nodes start with zero locked outputs, and the locked output list\n"
            "is always cleared (by virtue of process exit) when a node stops or fails.\n"
            "Also see the listunspent call\n"
            "\nArguments:\n"
            "1. unlock            (boolean, required) Whether to unlock (true) or lock (false) the specified transactions\n"
            "2. \"transactions\"  (string, optional) A json array of objects. Each object the txid (string) vout (numeric)\n"
            "     [           (json array of json objects)\n"
            "       {\n"
            "         \"txid\":\"id\",    (string) The transaction id\n"
            "         \"vout\": n         (numeric) The output number\n"
            "       }\n"
            "       ,...\n"
            "     ]\n"
            "\nResult:\n"
            "true|false    (boolean) Whether the command was successful or not\n"
            "\nExamples:\n"