MAINTAINERS: Remove entry for hw/s390x/s390-virtio-bus.[ch]

The files have been deleted recently, no need to keep these entries
anymore.
Signed-off-by: NThomas Huth <thuth@redhat.com>
Message-Id: <1456397100-22746-1-git-send-email-thuth@redhat.com>
Signed-off-by: NCornelia Huck <cornelia.huck@de.ibm.com>

MAINTAINERS

@@ -663,7 +663,6 @@ M: Alexander Graf <agraf@suse.de>
 S: Supported
 F: hw/char/sclp*.[hc]
 F: hw/s390x/
-X: hw/s390x/s390-virtio-bus.[ch]
 F: include/hw/s390x/
 F: pc-bios/s390-ccw/
 F: hw/watchdog/wdt_diag288.c