Assembler: Remove unneeded ref (#7576)

assembler/parts/header.html

@@ -11,7 +11,7 @@
 <!-- /wp:group -->
 
 <!-- wp:group {"style":{"spacing":{"blockGap":"var:preset|spacing|20"}},"layout":{"type":"flex","flexWrap":"nowrap"}} -->
-<div class="wp-block-group"><!-- wp:navigation {"ref":6,"className":"order-1 md:order-0"} /-->
+<div class="wp-block-group"><!-- wp:navigation {"className":"order-1 md:order-0"} /-->
 
 <!-- wp:buttons -->
 <div class="wp-block-buttons"><!-- wp:button -->