Readme.md: remove Go Report Card

It seems to be thrown off easily. We keep GolangCI instead as the source of truth.

Change-Id: I9a1170be8456fb6e6175f4b948b39a0c50f505b8
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/7264
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>
diff --git a/README.md b/README.md
index b17a09a..18910cb 100644
--- a/README.md
+++ b/README.md
@@ -15,7 +15,6 @@
 -->
 [![GoDoc](https://godoc.org/cuelang.org/go?status.svg)](https://godoc.org/cuelang.org/go)
 [![Github](https://github.com/cuelang/cue/workflows/Test/badge.svg)](https://github.com/cuelang/cue/actions)
-[![Go Report Card](https://goreportcard.com/badge/github.com/cuelang/cue)](https://goreportcard.com/report/github.com/cuelang/cue)
 [![GolangCI](https://golangci.com/badges/github.com/cuelang/cue.svg)](https://golangci.com/r/github.com/cuelang/cue)
 [![Go 1.13+](https://img.shields.io/badge/go-1.13-9cf.svg)](https://golang.org/dl/)
 [![platforms](https://img.shields.io/badge/platforms-linux|windows|macos-inactive.svg)]()