Remove references of CircleCI from the readme (facebook#49120)

Summary:
Pull Request resolved: facebook#49120

This change removes any reference of CircleCI from the READMEs in React Native

## Changelog
[Internal] - Remove CircleCI references

Reviewed By: cortinico, huntie

Differential Revision: D69047437

fbshipit-source-id: 602350372c1d869098be0c8da7cb3db2077474d8

README.md

@@ -13,9 +13,6 @@
   <a href="https://github.com/facebook/react-native/blob/HEAD/LICENSE">
     <img src="https://img.shields.io/badge/license-MIT-blue.svg" alt="React Native is released under the MIT license." />
   </a>
-  <a href="https://circleci.com/gh/facebook/react-native">
-    <img src="https://circleci.com/gh/facebook/react-native.svg?style=shield" alt="Current CircleCI build status." />
-  </a>
   <a href="https://www.npmjs.org/package/react-native">
     <img src="https://img.shields.io/npm/v/react-native?color=brightgreen&label=npm%20package" alt="Current npm package version." />
   </a>

packages/react-native/ReactAndroid/README.md

@@ -4,5 +4,5 @@ See the [Building from Source guide](https://reactnative.dev/contributing/how-to
 
 # Running tests
 
-When you submit a pull request CircleCI will automatically run all tests.
+When you submit a pull request, ci will automatically run all tests.
 To run tests locally, see [Testing guide](https://reactnative.dev/contributing/how-to-run-and-write-tests) on the React Native website.

scripts/releases-ci/README.md

@@ -1,6 +1,6 @@
 # scripts/releases-ci
 
-CI-only release scripts — intended to run from a CI workflow (CircleCI or GitHub Actions).
+CI-only release scripts — intended to run from a CI workflow (GitHub Actions).
 
 ## Commands