Free item memory when closing schematic window

This fires the dtor for each item on the screen, allowing us to properly
close and remove them from the connection graph

Fixes https://gitlab.com/kicad/code/kicad/-/issues/17961

(cherry picked from commit 9fbda137cb)

eeschema/sch_edit_frame.cpp

@@ -1055,7 +1055,7 @@ void SCH_EDIT_FRAME::doCloseWindow()
     // Make sure local settings are persisted
     SaveProjectLocalSettings();
 
-    Schematic().RootScreen()->Clear();
+    Schematic().RootScreen()->Clear( true );
 
     // all sub sheets are deleted, only the main sheet is usable
     GetCurrentSheet().clear();