test: titles in project previews (#45051)

* fix: trim titles before injecting into iframes

Surrounding whitespace isn't useful

* test: check preview iframe has correct title

cypress/plugins/index.js

@@ -26,8 +26,6 @@ module.exports = (on, config) => {
     }
   });
 
-  // Allows us to test the new curriculum before it's released:
-  config.env.SHOW_UPCOMING_CHANGES = process.env.SHOW_UPCOMING_CHANGES;
   config.env.API_LOCATION = process.env.API_LOCATION;
   return config;
 };