Collapse /etc/hhvm/fcgi into /etc/hhvm

Since we now only have one config file for each SAPI, it doesn't make sense to
have a separate directly for FastCGI stuff. Instead just keep /etc/hhvm/php.ini
and /etc/hhvm/fcgi.ini.

Change-Id: I6f60a14c052a275681556490264737d75305b74a