In `core_upgrade_preamble()`, `$alternate` is set then never used.

See #27882.


git-svn-id: https://develop.svn.wordpress.org/trunk@28314 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/update-core.php

@@ -182,7 +182,6 @@ function core_upgrade_preamble() {
 	}
 
 	echo '<ul class="core-updates">';
-	$alternate = true;
 	foreach( (array) $updates as $update ) {
 		echo '<li>';
 		list_core_update( $update );