Hide ConflatedBroadcastChannel private companion fields from public ABI

Unfortunately, Companion object reference remains public, even though
it exposes a private companion object type, see
https://youtrack.jetbrains.com/issue/KT-11567

Author: elizarov

binary-compatibility-validator/reference-public-api/kotlinx-coroutines-core.txt

@@ -563,10 +563,7 @@ public final class kotlinx/coroutines/channels/ClosedSendChannelException : java
 }
 
 public final class kotlinx/coroutines/channels/ConflatedBroadcastChannel : kotlinx/coroutines/channels/BroadcastChannel {
-	public static final field CLOSED Lkotlinx/coroutines/channels/ConflatedBroadcastChannel$Closed;
 	public static final field Companion Lkotlinx/coroutines/channels/ConflatedBroadcastChannel$Companion;
-	public static final field INITIAL_STATE Lkotlinx/coroutines/channels/ConflatedBroadcastChannel$State;
-	public static final field UNDEFINED Lkotlinx/coroutines/internal/Symbol;
 	public fun <init> ()V
 	public fun <init> (Ljava/lang/Object;)V
 	public fun cancel (Ljava/lang/Throwable;)Z

common/kotlinx-coroutines-core-common/src/channels/ConflatedBroadcastChannel.kt

@@ -45,14 +45,9 @@ public class ConflatedBroadcastChannel<E>() : BroadcastChannel<E> {
     private val onCloseHandler = atomic<Any?>(null)
 
     private companion object {
-        @JvmField
-        val CLOSED = Closed(null)
-
-        @JvmField
-        val UNDEFINED = Symbol("UNDEFINED")
-
-        @JvmField
-        val INITIAL_STATE = State<Any?>(UNDEFINED, null)
+        private val CLOSED = Closed(null)
+        private val UNDEFINED = Symbol("UNDEFINED")
+        private val INITIAL_STATE = State<Any?>(UNDEFINED, null)
     }
 
     private class State<E>(