Remove legacy restart code

runtime/vm/object.cc

Index: runtime/vm/object.cc
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index c18cd647b6591cef587275973eec9146bfa1ed19..0c3cdba4b2b28511728297bc395ce6f389c8eb6b 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -15407,7 +15407,6 @@ RawUnwindError* UnwindError::New(const String& message, Heap::Space space) {
   }
   result.set_message(message);
   result.set_is_user_initiated(false);
-  result.set_is_vm_restart(false);
   return result.raw();
 }
 
@@ -15422,11 +15421,6 @@ void UnwindError::set_is_user_initiated(bool value) const {
 }
 
 
-void UnwindError::set_is_vm_restart(bool value) const {
-  StoreNonPointer(&raw_ptr()->is_vm_restart_, value);
-}
-
-
 const char* UnwindError::ToErrorCString() const {
   const String& msg_str = String::Handle(message());
   return msg_str.ToCString();