remove item from schematic's connection graph on destruction

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

(cherry picked from commit 4920c6b00b)

eeschema/sch_item.cpp

@@ -33,6 +33,7 @@
 #include <sch_draw_panel.h>
 #include <sch_edit_frame.h>
 #include <schematic.h>
+#include <connection_graph.h>
 #include <trace_helpers.h>
 #include <general.h>
 #include <netclass.h>
@@ -88,6 +89,11 @@ SCH_ITEM::~SCH_ITEM()
 
     for( const auto& it : m_connection_map )
         delete it.second;
+
+    SCHEMATIC* sch = Schematic();
+
+    if( sch != nullptr )
+        sch->ConnectionGraph()->RemoveItem( this );
 }