R1:d5b006b2cc6f

Remove pcntl/php CLI setup checks

Summary:
As far as I know, we never actually need `php` to be available from the web UI. I think the history here is:

- Long ago, we checked for 'pcntl' as an extension during setup.
- Someone had an install where 'pcntl' was available from the CLI, but not the web UI. So we switched the check to use the CLI.
- Someone had an install where the CLI binary was php-fpm, which caused the 'pcntl' check to loop endlessly, so we added more checks.

But we don't actually…