Fix APCIterator syntax in \OC\Memcache\APCU::clear

see http://www.php.net/manual/en/apciterator.construct.php
Merge pull request #6610 from owncloud/apcu-clear

Fix APCIterator syntax in \OC\Memcache\APCu::clear
Merge remote-tracking branch 'upstream/master' into normalizer-intl