Remove legacy restart code

runtime/vm/dart_api_impl.cc

Index: runtime/vm/dart_api_impl.cc
diff --git a/runtime/vm/dart_api_impl.cc b/runtime/vm/dart_api_impl.cc
index 78363deb6d8eeb9af1cd0c811663678161b8f56e..ae24734af4e2b6821049799fc4bbd8ceba6ef689 100644
--- a/runtime/vm/dart_api_impl.cc
+++ b/runtime/vm/dart_api_impl.cc
@@ -809,13 +809,6 @@ DART_EXPORT bool Dart_IsFatalError(Dart_Handle object) {
 }
 
 
-DART_EXPORT bool Dart_IsVMRestartRequest(Dart_Handle handle) {
-  DARTSCOPE(Thread::Current());
-  const Object& obj = Object::Handle(Z, Api::UnwrapHandle(handle));
-  return (obj.IsUnwindError() && UnwindError::Cast(obj).is_vm_restart());
-}
-
-
 DART_EXPORT const char* Dart_GetError(Dart_Handle handle) {
   API_TIMELINE_DURATION;
   DARTSCOPE(Thread::Current());