Reduce visibility of ReactEventEmitter

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 ReactEventEmitter

Reviewed By: arushikesarwani94

Differential Revision: D49803292

fbshipit-source-id: 5c49555ce35ad10ee46bc3db3bc3bc83d8486a0d

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/events/ReactEventEmitter.java

@@ -19,7 +19,7 @@
 import com.facebook.react.uimanager.common.UIManagerType;
 import com.facebook.react.uimanager.common.ViewUtil;
 
-public class ReactEventEmitter implements RCTModernEventEmitter {
+class ReactEventEmitter implements RCTModernEventEmitter {
 
   private static final String TAG = "ReactEventEmitter";