phabricator: strip Ubuntu 12.04 (precise) support

iridium is trusty and presumably attempts to set up Labs test instances
will need to follow production. There's no reason to convolute our
manifests to support precise anymore.

The hardcoded php.ini isn't very future proof and should be probably be
replaced with something else (wmflib's php_ini? augeas?) but that should
follow in a separate commit.

Change-Id: Ib086e009ab71a0b3d0ac093a85388c52d863e801