Use common ThreadLocal declaration from stdlib

Author: elizarov

kotlinx-coroutines-core/common/src/EventLoop.common.kt

@@ -118,7 +118,7 @@ internal abstract class EventLoop : CoroutineDispatcher() {
     protected open fun shutdown() {}
 }
 
-@NativeThreadLocal
+@ThreadLocal
 internal object ThreadLocalEventLoop {
     private val ref = CommonThreadLocal<EventLoop?>()
 

kotlinx-coroutines-core/common/src/internal/ThreadLocal.common.kt

@@ -1,13 +1,9 @@
 /*
- * Copyright 2016-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ * Copyright 2016-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
  */
 
 package kotlinx.coroutines.internal
 
-@OptionalExpectation
-@UseExperimental(ExperimentalMultiplatform::class)
-internal expect annotation class NativeThreadLocal()
-
 internal expect class CommonThreadLocal<T>() {
     fun get(): T
     fun set(value: T)