### 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

{ "rawtransactions",    "fundrawtransaction",       &fundrawtransaction,       {"hexstring","options"} },
    { "hidden",             "resendwallettransactions", &resendwallettransactions, {} },
    { "wallet",             "abandontransaction",       &abandontransaction,       {"txid"} },
    { "wallet",             "abortrescan",              &abortrescan,              {} },
    { "wallet",             "addmultisigaddress",       &addmultisigaddress,       {"nrequired","keys","account"} },
    { "wallet",             "addwitnessaddress",        &addwitnessaddress,        {"address","p2sh"} },
    { "wallet",             "backupwallet",             &backupwallet,             {"destination"} },
    { "wallet",             "bumpfee",                  &bumpfee,                  {"txid", "options"} },
    { "wallet",             "dumpprivkey",              &dumpprivkey,              {"address"}  },
    { "wallet",             "dumpwallet",               &dumpwallet,               {"filename"} },
    { "wallet",             "encryptwallet",            &encryptwallet,            {"passphrase"} },
    { "wallet",             "getaccountaddress",        &getaccountaddress,        {"account"} },
    { "wallet",             "getaccount",               &getaccount,               {"address"} },
    { "wallet",             "getaddressesbyaccount",    &getaddressesbyaccount,    {"account"} },
    { "wallet",             "getbalance",               &getbalance,               {"account","minconf","include_watchonly"} },
    { "wallet",             "getnewaddress",            &getnewaddress,            {"account"} },
    { "wallet",             "getrawchangeaddress",      &getrawchangeaddress,      {} },
    { "wallet",             "getreceivedbyaccount",     &getreceivedbyaccount,     {"account","minconf"} },
    { "wallet",             "getreceivedbyaddress",     &getreceivedbyaddress,     {"address","minconf"} },
    { "wallet",             "gettransaction",           &gettransaction,           {"txid","include_watchonly"} },
    { "wallet",             "getunconfirmedbalance",    &getunconfirmedbalance,    {} },
    { "wallet",             "getwalletinfo",            &getwalletinfo,            {} },
    { "wallet",             "importmulti",              &importmulti,              {"requests","options"} },
    { "wallet",             "importprivkey",            &importprivkey,            {"privkey","label","rescan"} },
    { "wallet",             "importwallet",             &importwallet,             {"filename"} },
    { "wallet",             "importaddress",            &importaddress,            {"address","label","rescan","p2sh"} },
    { "wallet",             "importprunedfunds",        &importprunedfunds,        {"rawtransaction","txoutproof"} },
    { "wallet",             "importpubkey",             &importpubkey,             {"pubkey","label","rescan"} },
    { "wallet",             "keypoolrefill",            &keypoolrefill,            {"newsize"} },