Add unavailable options to hidden options category

Options that are not available (but known in the source code) will
cause an error if they are specified.
Make these options "available" by adding them to the hidden options
category to prevent conf files from failing when shared between binaries
that have different options available.

src/bitcoind.cpp

@@ -62,9 +62,6 @@ static bool AppInit(int argc, char* argv[])
     //
     // If Qt is used, parameters/bitcoin.conf are parsed in qt/bitcoin.cpp's main()
     SetupServerArgs();
-#if HAVE_DECL_DAEMON
-    gArgs.AddArg("-daemon", "Run in the background as a daemon and accept commands", false, OptionsCategory::OPTIONS);
-#endif
     std::string error;
     if (!gArgs.ParseParameters(argc, argv, error)) {
         fprintf(stderr, "Error parsing command line arguments: %s\n", error.c_str());