revert #273; it breaks multisite keys

Author: tillkruss

includes/object-cache.php

@@ -1779,18 +1779,10 @@ function ( $keys ) {
      * @return  string
      */
     public function build_key( $key, $group = 'default' ) {
-        static $keys = [];
-
         if ( empty( $group ) ) {
             $group = 'default';
         }
 
-        $key_index = "{$key}:{$group}";
-
-        if ( isset( $keys[ $key_index ] ) ) {
-            return $keys[ $key_index ];
-        }
-
         $salt = defined( 'WP_REDIS_PREFIX' ) ? trim( WP_REDIS_PREFIX ) : '';
         $prefix = $this->is_global_group( $group ) ? $this->global_prefix : $this->blog_prefix;
 
@@ -1799,7 +1791,7 @@ public function build_key( $key, $group = 'default' ) {
 
         $prefix = trim( $prefix, '_-:$' );
 
-        return $keys[ $key_index ] = "{$salt}{$prefix}:{$group}:{$key}";
+        return "{$salt}{$prefix}:{$group}:{$key}";
     }
 
     /**