fixup! Remove the symmetric helper $bookmark_start since it's not necessary

Author: dmsnell

src/wp-includes/html-api/class-wp-html-tag-processor.php

@@ -1651,7 +1651,7 @@ private function apply_attributes_updates( $shift_this_point = 0 ) {
 		 * replacements adjust offsets in the input document.
 		 */
 		foreach ( $this->bookmarks as $bookmark_name => $bookmark ) {
-			$bookmark_end   = $bookmark_start + $bookmark->length;
+			$bookmark_end   = $bookmark->start + $bookmark->length;
 
 			/*
 			 * Each lexical update which appears before the bookmark's endpoints