APCu is now provided by base image

Summary: We moved the APCu extension to the nasqueron/php-fpm base image.

Test Plan: php -l to ensure APCu is loaded

Reviewers: Kaliiixx

Subscribers: Nasqueron Docker deployment squad

Projects: Docker images

Maniphest Tasks: T604

Differential Revision: http://devcentral.nasqueron.org/D98