blockdev: no need to drain+flush in hmp_drive_del

bdrv_close already does that, and in fact hmp_drive_del would need
another drain after the flush (which bdrv_close does).  So remove
the duplication.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Reviewed-by: NAlberto Garcia <berto@igalia.com>
Reviewed-by: NFam Zheng <famz@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Message-id: 1432822629-25401-1-git-send-email-pbonzini@redhat.com
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

blockdev.c

@@ -2167,9 +2167,6 @@ void hmp_drive_del(Monitor *mon, const QDict *qdict)
         return;
     }
 
-    /* quiesce block driver; prevent further io */
-    bdrv_drain_all();
-    bdrv_flush(bs);
     bdrv_close(bs);
 
     /* if we have a device attached to this BlockDriverState