Reduce visibility of CountingOutputStream

Summary:
In an attempt to reduce footprint of React Native Android public APIs we are reducing visibility of classes and interfaces that are not meant to be used publicly OR are public but have no usages.
As part of our analysis, which involved looking for usages inside the Meta codebase and code search in OSS, we've detected that this class/interface is public but it's not used from other packages.

If you are using this class or interface please comment in this PR and we will restate the public access.

bypass-github-export-checks

changelog: [Android][Changed] Reducing visibility of CountingOutputStream

Reviewed By: arushikesarwani94

Differential Revision: D49803284

fbshipit-source-id: fb411c6f6335c0bf4b42f8b87c4cdb3e01fc6e7c

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/modules/network/CountingOutputStream.java

@@ -26,7 +26,7 @@
  * @author Chris Nokleberg
  * @since 1.0
  */
-public class CountingOutputStream extends FilterOutputStream {
+class CountingOutputStream extends FilterOutputStream {
 
   private long mCount;