[PyTorch] Remove unnecessary iostream includes in headers (#61500)

[PyTorch] Remove unnecessary iostream includes in headers (#61500)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/61500

libstdc++ defines a static variable called `std::__ioinit` in iostream that adds global constructor size overhead to each translation that includes iostream. To reduce the size overhead from that, we can often include ostream instead.
ghstack-source-id: 136163529

Test Plan: buildsizebot some mobile apps

Reviewed By: dhruvbird

Differential Revision: D29648016

fbshipit-source-id: 9c3139712c71248513cc5032d21e77f3ecbae8fe