Remove obsoleted functions from Utils::Gui namespace

`widget` parameter is kept for now to avoid major disruption for other PR.
Also add comments for loading svg images.

PR #16613.

src/gui/autoexpandabledialog.cpp

@@ -101,6 +101,6 @@ void AutoExpandableDialog::showEvent(QShowEvent *e)
     if (wd > width())
     {
         QSize size = {width() - m_ui->verticalLayout->sizeHint().width() + wd, height()};
-        Utils::Gui::resize(this, size);
+        resize(size);
     }
 }