Remove legacy Supabase OAuth functions and update plugin

Remove legacy Supabase OAuth functions and update plugin Deleted all Supabase edge function source files for Xero OAuth and license validation, as these are now managed externally. Updated .gitignore to exclude the .github directory. In variables.php, removed default Xero client ID/secret values for improved security. Updated plugin author information and set WXL_DEBUG to false by default in woo-xero-sync.php. Also removed obsolete debug logging from the main plugin file.