Removed extra non working SharedImmutable annotations (#1892)

Author: LepilkinaElena

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

@@ -47,9 +47,7 @@ public class ConflatedBroadcastChannel<E>() : BroadcastChannel<E> {
     private val onCloseHandler = atomic<Any?>(null)
 
     private companion object {
-        @SharedImmutable
         private val CLOSED = Closed(null)
-        @SharedImmutable
         private val UNDEFINED = Symbol("UNDEFINED")
         private val INITIAL_STATE = State<Any?>(UNDEFINED, null)
     }

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

@@ -31,7 +31,6 @@ internal open class ConflatedChannel<E> : AbstractChannel<E>() {
     private var value: Any? = EMPTY
 
     private companion object {
-        @SharedImmutable
         private val EMPTY = Symbol("EMPTY")
     }