Clean up nets from items when deleting in the inspector

Fixes https://gitlab.com/kicad/code/kicad/-/issues/8162

pcbnew/board.cpp

@@ -671,7 +671,28 @@ void BOARD::Remove( BOARD_ITEM* aBoardItem, REMOVE_MODE aRemoveMode )
     {
     case PCB_NETINFO_T:
     {
-        NETINFO_ITEM* item = (NETINFO_ITEM*) aBoardItem;
+        NETINFO_ITEM* item        = static_cast<NETINFO_ITEM*>( aBoardItem );
+        NETINFO_ITEM* unconnected = m_NetInfo.GetNetItem( NETINFO_LIST::UNCONNECTED );
+        int           removedCode = item->GetNetCode();
+
+        for( FOOTPRINT* fp : m_footprints )
+        {
+            for( PAD* pad : fp->Pads() )
+            {
+                if( pad->GetNetCode() == removedCode )
+                    pad->SetNet( unconnected );
+            }
+        }
+
+        for( ZONE* zone : m_zones )
+        {
+            if( zone->GetNetCode() == removedCode )
+                zone->SetNet( unconnected );
+        }
+
+        for( TRACK* track : TracksInNet( removedCode ) )
+            track->SetNet( unconnected );
+
         m_NetInfo.RemoveNet( item );
         break;
     }

pcbnew/dialogs/dialog_net_inspector.cpp

@@ -1928,6 +1928,19 @@ void DIALOG_NET_INSPECTOR::onDeleteNet( wxCommandEvent& aEvent )
                         || IsOK( this, wxString::Format( _( "Net '%s' is in use.  Delete anyway?" ),
                                                          i->GetNetName() ) ) )
                 {
+                    // This is a bit hacky, but it will do for now, since this is the only path
+                    // outside the netlist updater where you can remove a net from a BOARD.
+                    int removedCode = i->GetNetCode();
+
+                    m_frame->GetCanvas()->GetView()->UpdateAllItemsConditionally( KIGFX::REPAINT,
+                            [removedCode]( KIGFX::VIEW_ITEM* aItem ) -> bool
+                            {
+                                if( auto bci = dynamic_cast<BOARD_CONNECTED_ITEM*>( aItem ) )
+                                    return bci->GetNetCode() == removedCode;
+
+                                return false;
+                            } );
+
                     m_brd->Remove( i->GetNet() );
                     m_frame->OnModify();