Remove no longer existing buildkite link to rules-cc-plus-bazelisk-migrate from rules_cc/README

PiperOrigin-RevId: 774668912
Change-Id: I007e40c738d548e370dc7e73d700c94a9515733b

Author: pzembrod

README.md

@@ -1,7 +1,6 @@
 # C++ rules for Bazel
 
 * Postsubmit [![Build status](https://badge.buildkite.com/f03592ae2d7d25a2abc2a2ba776e704823fa17fd3e061f5103.svg?branch=main)](https://buildkite.com/bazel/rules-cc)
-* Postsubmit + Current Bazel Incompatible flags [![Build status](https://badge.buildkite.com/5ba709cc33e5855078a1f8570adcf8e0a78ea93591bc0b4e81.svg?branch=master)](https://buildkite.com/bazel/rules-cc-plus-bazelisk-migrate)
 
 This repository contains a Starlark implementation of C++ rules in Bazel.