qxl: drop update_displaychangelistener call for secondary qxl devices

Commit 3dcadce5 added three
update_displaychangelistener call sites:

Two for primary qxl cards, when entering/leaving vga mode, which are
correct.

One for secondary qxl cards, which is wrong because we don't register
a displaychangelistener in the first place for secondary cards.

Remove it.
Reported-by: NBrad Campbell <lists2009@fnarfbargle.com>
Tested-by: NBrad Campbell <lists2009@fnarfbargle.com>
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

hw/display/qxl.c

@@ -1147,7 +1147,6 @@ static void qxl_soft_reset(PCIQXLDevice *d)
         qxl_enter_vga_mode(d);
     } else {
         d->mode = QXL_MODE_UNDEFINED;
-        update_displaychangelistener(&d->ssd.dcl, GUI_REFRESH_INTERVAL_IDLE);
     }
 }