sna/present: Drop TearFree assert at the end of unflip

There are more reasons than just TearFree as to why the shadow may be
disabled (such as no outputs), so without taking those into account the
assert is bogus.

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

src/sna/sna_present.c

@@ -899,8 +899,6 @@ notify:
 		     swap->tv_sec, swap->tv_usec, (long long)swap->msc,
 		     (long long)event_id));
 		present_event_notify(event_id, swap_ust(swap), swap->msc);
-		assert(!(sna->flags & SNA_TEAR_FREE) ||
-		       sna->mode.shadow_enabled);
 		return;
 	}