Set some defaults back to correctness.

Summary:
There were a few defaults that got changed when porting to PHP. Most of them
seem to be accidental, so this diff sets them back to correctness.

Test Plan:
  php> require '../libphutil/src/__phutil_library_init__.php';
  php> require 'src/__phutil_library_init__.php'
  php> $a = PhabricatorApplicationConfigOptions::loadAllOptions()
  php> $b = require 'conf/default.conf.php';
  php> $x = array();
  php> foreach($a as $key => $obj) { $x[$key] = $obj->getDefault(); }
  php> foreach($x as $key => $default) { if ($b[$key] != $default) { echo "$key has different default.\n"; } }

  log.access.format has different default.
  (seems to be intentional)

  PHP Notice:  Undefined index: phabricator.env in /usr/lib/python2.7/site-packages/phpsh/phpsh.php(577) : eval()'d code on line 1
  (no longer in config file)

  PHP Notice:  Undefined index: test.value in /usr/lib/python2.7/site-packages/phpsh/phpsh.php(577) : eval()'d code on line 1
  (not in config file)

  metamta.default-address has different default.
  (intentional)

  metamta.domain has different default.
  (intentional)

  PHP Notice:  Undefined index: phid.external-loaders in /usr/lib/python2.7/site-packages/phpsh/phpsh.php(577) : eval()'d code on line 1
  (no longer in config file)

  phame.skins has different default.
  (fixed in D4618)

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2255

Differential Revision: https://secure.phabricator.com/D4621