svga: remove duplicated code

list_del unconditionally sets "next" and "prev" to NULL.

Signed-off-by: Marcin Ślusarz <marcin.slusarz@intel.com>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8110>

src/gallium/drivers/svga/svga_resource_buffer_upload.c

@@ -730,9 +730,6 @@ svga_buffer_upload_flush(struct svga_context *svga, struct svga_buffer *sbuf)
 
    assert(sbuf->head.prev && sbuf->head.next);
    list_del(&sbuf->head);  /* remove from svga->dirty_buffers list */
-#ifdef DEBUG
-   sbuf->head.next = sbuf->head.prev = NULL;
-#endif
    sbuf->dma.pending = FALSE;
    sbuf->dma.flags.discard = FALSE;
    sbuf->dma.flags.unsynchronized = FALSE;