Removed "code" property from global error variable

refs https://github.com/TryGhost/Toolbox/issues/406
refs b2a3e03ef3

- The "code" property in the global "error" variable (accessible via {{error.*}}) has been long deprecated - time to go, bye!
- When {{code}} or {{error.code}} helpers are used in the templates they will output an empty string from now on. Use {{statusCode}} instead!

ghost/core/core/frontend/web/middleware/error-handler.js

@@ -47,8 +47,6 @@ const themeErrorRenderer = (err, req, res, next) => {
     // Format Data
     const data = {
         message: err.message,
-        // @deprecated Remove in Ghost 5.0
-        code: err.statusCode,
         statusCode: err.statusCode,
         errorDetails: err.errorDetails || []
     };