Move main thread check to legacy mm (#4483)

kotlin-native/runtime/src/main/cpp/Runtime.cpp

@@ -69,7 +69,6 @@ KBoolean g_checkLeakedCleaners = KonanNeedDebugInfo;
 constexpr RuntimeState* kInvalidRuntime = nullptr;
 
 THREAD_LOCAL_VARIABLE RuntimeState* runtimeState = kInvalidRuntime;
-THREAD_LOCAL_VARIABLE int isMainThread = 0;
 
 inline bool isValidRuntime() {
   return ::runtimeState != kInvalidRuntime;
@@ -88,7 +87,6 @@ RuntimeState* initRuntime() {
   bool firstRuntime = atomicAdd(&aliveRuntimesCount, 1) == 1;
   // Keep global variables in state as well.
   if (firstRuntime) {
-    isMainThread = 1;
     konan::consoleInit();
 #if KONAN_OBJC_INTEROP
     Kotlin_ObjCExport_initialize();
@@ -151,11 +149,6 @@ void Kotlin_deinitRuntimeIfNeeded() {
   }
 }
 
-void CheckIsMainThread() {
-  if (!isMainThread)
-    ThrowIncorrectDereferenceException();
-}
-
 KInt Konan_Platform_canAccessUnaligned() {
 #if KONAN_NO_UNALIGNED_ACCESS
   return 0;