qt: Replace `GUIUtil::ObjectInvoke()` with `QMetaObject::invokeMethod()`

The `GUIUtil::ObjectInvoke()` template function was a replacement of
the `QMetaObject::invokeMethod()` functor overload which is available
in Qt 5.10+.

No behavior change.

src/qt/initexecutor.cpp

@@ -5,13 +5,13 @@
 #include <qt/initexecutor.h>
 
 #include <interfaces/node.h>
-#include <qt/guiutil.h>
 #include <util/system.h>
 #include <util/threadnames.h>
 
 #include <exception>
 
 #include <QDebug>
+#include <QMetaObject>
 #include <QObject>
 #include <QString>
 #include <QThread>
@@ -39,7 +39,7 @@ void InitExecutor::handleRunawayException(const std::exception* e)
 
 void InitExecutor::initialize()
 {
-    GUIUtil::ObjectInvoke(&m_context, [this] {
+    QMetaObject::invokeMethod(&m_context, [this] {
         try {
             util::ThreadRename("qt-init");
             qDebug() << "Running initialization in thread";
@@ -56,7 +56,7 @@ void InitExecutor::initialize()
 
 void InitExecutor::shutdown()
 {
-    GUIUtil::ObjectInvoke(&m_context, [this] {
+    QMetaObject::invokeMethod(&m_context, [this] {
         try {
             qDebug() << "Running Shutdown in thread";
             m_node.appShutdown();

src/qt/walletcontroller.cpp

@@ -24,6 +24,7 @@
 
 #include <QApplication>
 #include <QMessageBox>
+#include <QMetaObject>
 #include <QMutexLocker>
 #include <QThread>
 #include <QTimer>
@@ -135,7 +136,7 @@ WalletModel* WalletController::getOrCreateWallet(std::unique_ptr<interfaces::Wal
     // handled on the GUI event loop.
     wallet_model->moveToThread(thread());
     // setParent(parent) must be called in the thread which created the parent object. More details in #18948.
-    GUIUtil::ObjectInvoke(this, [wallet_model, this] {
+    QMetaObject::invokeMethod(this, [wallet_model, this] {
         wallet_model->setParent(this);
     }, GUIUtil::blockingGUIThreadConnection());