Remove powered by Vercel

Author: marcoacierno

README.md

@@ -51,5 +51,3 @@ Repos used by this project are in separate repositories.
 | ------------- | ------------------------------------------------------- | ------------------------------------------------------ |
 | Pretix Extended API | Pretix plugin to expose more APIs                   | https://github.com/pythonitalia/pretix-plugin-extended-api |
 | Pretix Attendance certificate | Pretix plugin to generate and send Attendance certificates | https://github.com/pythonitalia/pretix-plugin-attendance-certificate |
-
-[<img src="https://www.datocms-assets.com/31049/1618983297-powered-by-vercel.svg">](https://vercel.com?utm_source=python-italia&utm_campaign=oss)