Delete inaccurate comments. (#4139)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/4139

This comment is not accurate anymore since D47523786.

Instead of fixing this comment, I think it is better to just delete it because it is error prone. It becomes inaccurate again if data loader implementation gets moved again.
ghstack-source-id: 232554179
exported-using-ghexport

Reviewed By: dbort

Differential Revision: D59254811

fbshipit-source-id: 15c765dd7350d8b0fefce6b93245bfaab403f7fa