gpu: Remove warning

The warning gets triggered by rounding errors.

In particular when using fractional scales, the final tile may end up
not accurately matching the computed final value (in the example I was
debugging it was computing 1 vs 1.00000036 for the final tile index,
but that result computed a 0px wide tile size.
And for that tile size we hit that exit condition.

gsk/gpu/gskgpunodeprocessor.c

@@ -3206,8 +3206,7 @@ gsk_gpu_node_processor_repeat_tile (GskGpuNodeProcessor    *self,
                                               - y * child_bounds->size.height));
   if (!gsk_rect_intersection (&offset_rect, child_bounds, &clipped_child_bounds))
     {
-      /* The math has gone wrong probably, someone should look at this. */
-      g_warn_if_reached ();
+      /* rounding error hits again */
       return;
     }