Revert "Fix bug #66568: the second arg for unserialize is optional." as we already reverted the introduction of the second arg.

This reverts commit aefc8f22b35999624f3a579696cf68b389f41ae8.

Conflicts:
	NEWS
Merge branch 'PHP-5.6'

* PHP-5.6:
  Revert "Fix bug #66568: the second arg for unserialize is optional." as we already reverted the introduction of the second arg.