pcbnew: Check netlist settings in proper spot

We have _two_ settings that independently control whether the netlist is
updated by timestamp.  One in the NETLIST object and one in the
NETLIST_UPDATER object.  It looks like we are phasing one out but the
commit was not complete.

Fixes: lp:1828754
* https://bugs.launchpad.net/kicad/+bug/1828754

pcbnew/board_netlist_updater.cpp

@@ -723,7 +723,7 @@ bool BOARD_NETLIST_UPDATER::UpdateNetlist( NETLIST& aNetlist )
 
             if( footprint )
             {
-                if( aNetlist.IsFindByTimeStamp() )
+                if( m_lookupByTimestamp )
                     match = footprint->GetPath() == component->GetTimeStamp();
                 else
                     match = footprint->GetReference().CmpNoCase( component->GetReference() ) == 0;