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/trackerentriesdialog.cpp

@@ -110,5 +110,5 @@ void TrackerEntriesDialog::saveSettings()
 
 void TrackerEntriesDialog::loadSettings()
 {
-    Utils::Gui::resize(this, m_storeDialogSize);
+    resize(m_storeDialogSize);
 }