Revert "LevelBar: Avoid unnecessarily copying allocation"

This reverts commit d5e25be9bc.

It doesn't build.

gtk/gtklevelbar.c

@@ -434,8 +434,9 @@ gtk_level_bar_allocate_trough_continuous (GtkLevelBar *self,
   inverted = gtk_level_bar_get_real_inverted (self);
 
   /* allocate the empty (unfilled) part */
+  block_area = *allocation;
   gtk_widget_size_allocate (self->priv->block_widget[inverted ? 0 : 1],
-                            allocation
+                            &block_area,
                             baseline,
                             out_clip);