qxl: drop update_displaychangelistener call for secondary qxl devices

Commit 3dcadce5076d4b42fa395c39662d65e050b77784 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: Brad Campbell <lists2009@fnarfbargle.com>
Tested-by: Brad Campbell <lists2009@fnarfbargle.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

hw/display/qxl.c

diff --git a/hw/display/qxl.c b/hw/display/qxl.c
index 94ff52a..762f75d 100644
--- a/hw/display/qxl.c
+++ b/hw/display/qxl.c
@@ -1147,7 +1147,6 @@
         qxl_enter_vga_mode(d);
     } else {
         d->mode = QXL_MODE_UNDEFINED;
-        update_displaychangelistener(&d->ssd.dcl, GUI_REFRESH_INTERVAL_IDLE);
     }
 }