[ci] Remove scorecard action (flutter#7450)

Removes scorecard, as it's currently not providing enough value in this
repo to maintain it.

Fixes flutter#153626

README.md

@@ -2,7 +2,6 @@
 
 [![Release Status](https://github.com/flutter/packages/actions/workflows/release.yml/badge.svg)](https://github.com/flutter/packages/actions/workflows/release.yml)
 [![Flutter CI Status](https://flutter-dashboard.appspot.com/api/public/build-status-badge?repo=packages)](https://flutter-dashboard.appspot.com/#/build?repo=packages)
-[![OpenSSF Scorecard](https://api.securityscorecards.dev/projects/github.com/flutter/packages/badge)](https://deps.dev/project/github/flutter%2Fpackages)
 
 This repo is a companion repo to the main [flutter repo](
 https://github.com/flutter/flutter). It contains the source code for Flutter's