### 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() > 4)
        throw std::runtime_error(
            "listtransactions ( \"account\" count skip include_watchonly)\n"
            "\nReturns up to 'count' most recent transactions skipping the first 'from' transactions for account 'account'.\n"
            "\nArguments:\n"
            "1. \"account\"    (string, optional) DEPRECATED. The account name. Should be \"*\".\n"
            "2. count          (numeric, optional, default=10) The number of transactions to return\n"
            "3. skip           (numeric, optional, default=0) The number of transactions to skip\n"
            "4. include_watchonly (bool, optional, default=false) Include transactions to watch-only addresses (see 'importaddress')\n"
            "\nResult:\n"
            "[\n"
            "  {\n"
            "    \"account\":\"accountname\",       (string) DEPRECATED. The account name associated with the transaction. \n"
            "                                                It will be \"\" for the default account.\n"
            "    \"address\":\"address\",    (string) The bitcoin address of the transaction. Not present for \n"
            "                                                move transactions (category = move).\n"
            "    \"category\":\"send|receive|move\", (string) The transaction category. 'move' is a local (off blockchain)\n"
            "                                                transaction between accounts, and not associated with an address,\n"
            "                                                transaction id or block. 'send' and 'receive' transactions are \n"