Reduce visibility of ProgressRequestBody

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.

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

Reviewed By: arushikesarwani94

Differential Revision: D49803278

fbshipit-source-id: d049b97dbb0124274830a14d18c30d0574f04532

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

@@ -14,7 +14,7 @@
 import okio.Okio;
 import okio.Sink;
 
-public class ProgressRequestBody extends RequestBody {
+class ProgressRequestBody extends RequestBody {
 
   private final RequestBody mRequestBody;
   private final ProgressListener mProgressListener;