Don't reveal whether password is <20 or >20 characters in RPC

As discussed on IRC.

It seems bad to base a decision to delay based on the password length,
as it leaks a small amount of information.

src/rpcserver.cpp

@@ -849,10 +849,9 @@ static bool HTTPReq_JSONRPC(AcceptedConnection *conn,
     if (!HTTPAuthorized(mapHeaders))
     {
         LogPrintf("ThreadRPCServer incorrect password attempt from %s\n", conn->peer_address_to_string());
-        /* Deter brute-forcing short passwords.
+        /* Deter brute-forcing
            If this results in a DoS the user really
            shouldn't have their RPC port exposed. */
-        if (mapArgs["-rpcpassword"].size() < 20)
         MilliSleep(250);
 
         conn->stream() << HTTPError(HTTP_UNAUTHORIZED, false) << std::flush;