Remove use of CRPCTable::appendCommand in wallet code

This commit does not change behavior.

src/interfaces/chain.h

@@ -16,6 +16,7 @@
 
 class CBlock;
 class CFeeRate;
+class CRPCCommand;
 class CScheduler;
 class CValidationState;
 class uint256;
@@ -243,6 +244,10 @@ public:
 
     //! Wait for pending notifications to be handled.
     virtual void waitForNotifications() = 0;
+
+    //! Register handler for RPC. Command is not copied, so reference
+    //! needs to remain valid until Handler is disconnected.
+    virtual std::unique_ptr<Handler> handleRpc(const CRPCCommand& command) = 0;
 };
 
 //! Interface to let node manage chain clients (wallets, or maybe tools for