chore: Cleanup to be consistent with other sites 🦭

[darcywong00]

Relates to keymanapp/keyman.com#403

To facilitate upcoming deployment, this does some cleanup to be consistent with other sites.

• Rename /_include to /_includes
• Remove composer scripts (test action handled by build.sh)
• Add /control_info.php to troubleshoot tier
• Cleanup .htaccess