vdpau/display: do not set background colour

This interferes with overlay-based outputs, and serves no useful
purpose for VLC since the video frames are always fully opaque.

(cherry picked from commit 345fa6c345d839ff3bec9c0f455e0eb2034f0369)

modules/hw/vdpau/display.c

@@ -661,9 +661,6 @@ static int Open(vlc_object_t *obj)
         goto error;
     }
 
-    VdpColor black = { 0.f, 0.f, 0.f, 1.f };
-    vdp_presentation_queue_set_background_color(sys->vdp, sys->queue, &black);
-
     sys->cursor = XCB_cursor_Create(sys->conn, screen);
     sys->pool = NULL;