Networks and Sites: Remove obsolete code from wp-activate.php.

The `WP_Object_Cache::$cache_enabled` property does not exist in core as of WordPress 2.5, and has no meaningful usage in external object cache implementations.

This check was originally added for debugging purposes, and is now a remnant from the WPMU merge.

Follow-up to [6539], [https://mu.trac.wordpress.org/changeset/1298 mu:1298], [https://mu.trac.wordpress.org/changeset/1319 mu:1319], [12603].

Props skithund, jrf, snehapatil02, debarghyabanerjee, tillkruess, audrasjb, spacedmonkey, desrosj, rollybueno, SergeyBiryukov.
Fixes #61675.

git-svn-id: https://develop.svn.wordpress.org/trunk@60914 602fd350-edb4-49c9-b593-d223f7449a82

Author: SergeyBiryukov

src/wp-activate.php

@@ -64,10 +64,6 @@
 
 nocache_headers();
 
-if ( is_object( $wp_object_cache ) ) {
-	$wp_object_cache->cache_enabled = false;
-}
-
 // Fix for page title.
 $wp_query->is_404 = false;