chore(docs): remove unused PlanBox component and import

Author: hannesrudolph

docs/roo-code-cloud/billing-subscriptions.mdx

@@ -12,7 +12,6 @@ image: /img/social-share.jpg
 ---
 
 import Codicon from '@site/src/components/Codicon';
-import PlanBox from '@site/src/components/PlanBox';
 
 # Subscriptions & Billing