Revert "phpfpm service: restructured pool configuration"

This reverts commit 6b3f5b5a because it
introduced a non-backwards compatible change in the phpfpm interface,
without really needing to. The new interface, if needed, can be re-added
alongside the old interface.

Commit 98e419c0 ("tt-rss service: init at 16.3")
depends on the new interface, so this commit updates the tt-rss service
to work with the old services.phpfpm.poolConfigs interface.