Revert "Optimize APC objects and collections by defining an APCCollection class and increasing the number of APCObject vs serialized objects"

Summary: This reverts commit 9678712bfce1bdd3b607feb7dd2328410dc45331.

This is being reverted because it doesn't quite respect the behavior for
__sleep().

Reviewed By: alexanderm, bertrand, smith

Differential Revision: D1475357