Rework deinit sequence to avoid bogus leak detector warnings.

runtime/src/main/cpp/Porting.cpp

@@ -127,7 +127,7 @@ void onThreadExit(void (*destructor)()) {
 #ifdef KONAN_WASM
   // No way to do that.
 #else
-  ::atexit(destructor);
+#error "How to do onThreadExit()?"
 #endif
 #else  // !KONAN_NO_THREADS
   // We cannot use pthread_cleanup_push() as it is lexical scope bound.

runtime/src/main/cpp/Runtime.cpp

@@ -82,15 +82,6 @@ void Kotlin_initRuntimeIfNeeded() {
     runtimeState = initRuntime();
     // Register runtime deinit function at thread cleanup.
     konan::onThreadExit(Kotlin_deinitRuntimeIfNeeded);
-#ifndef KONAN_WASM
-    // `onThreadExit` doesn't work on main thread, use `atexit`:
-
-    static bool deinitScheduledAtexit = false;
-    if (!deinitScheduledAtexit) {
-      deinitScheduledAtexit = true; // Having data race is OK here.
-      ::atexit(Kotlin_deinitRuntimeIfNeeded);
-    }
-#endif
   }
 }