sna/dri2: Remove stale active buffer assert

Since the DRI2BufferPtr destruction may be delayed, by the time we do
free it, the state may no longer be accurate. (At this level at least,
there is a later assertion to the same regard just as we think we are
releasing the buffer.)

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

src/sna/sna_dri2.c

@@ -821,7 +821,6 @@ sna_dri2_cache_bo(struct sna *sna,
 	return;
 
 err:
-	assert(bo->active_scanout == 0 || bo->scanout);
 	kgem_bo_destroy(&sna->kgem, bo);
 }