[bitcoin/bitcoin] Refactoring CRPCCommand with enum category (#13945)

isghe commented on this pull request.

> @@ -0,0 +1,32 @@
+// Copyright (c) 2018 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+enum class RPCCategory

In the way they are implemented and used, there seems to be no relationship between `RPCCategory` and` OptionsCategory`.