refactor: Cleanup headers from walletmodel.h

src/qt/receiverequestdialog.h

@@ -6,10 +6,11 @@
 #define BITCOIN_QT_RECEIVEREQUESTDIALOG_H
 
 #include <qt/sendcoinsrecipient.h>
-#include <qt/walletmodel.h>
 
 #include <QDialog>
 
+class WalletModel;
+
 namespace Ui {
     class ReceiveRequestDialog;
 }