C++ unregister_module function for Module (#26088)
Summary:
This PR adds ```unregister_module``` to ```nn::Module``` and ```erase``` function to ```OrderedDict```.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/26088
Differential Revision: D17360058
Pulled By: yf225
fbshipit-source-id: f1f375b4751317da85b8da1458e092fe2405ceec
