Follows-up bec7e8287c. The comment "Can be removed once we require
PHP >= 5.4.28, 5.5.12, 5.6.0" relies on some assumptions that might
later prove to be incorrect:
* That the fix won't be reverted from any of those PHP versions
(e.g. if deemed to break BC)
* That the bug will be fixed in PECL jsonc and jsond, as well as in
HHVM
* That we don't need to support older versions of those once we
require one of the mentioned PHP versions
Change-Id: I67034c561d54d37dee961ada8c9cf5ccfd113da1
b9a12b0b33