Remove the code that handles $_SESSION['cache_expiration']

DrupalDatabaseCache uses $_SESSION['cache_expiration'] to delay the removal of items from the cache. DrupalApcCache does not need to use $_SESSION['cache_expiration'] because items are automatically removed by the APCu extension when the TTL value required by apcu_store() is passed.

Any code using $_SESSION['cache_expiration'] needs to be removed.