Add unsafeRemoveAttr and unsafeRemoveSlot to ivalue::Object (#29048)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/29048
In order to support remove_attribute in module, we need to support
remove slot in ivalue::Object, it's caller's responsiblity to gaurantee
the safety of the remove operation
Test Plan:
build/bin/test_jit
Imported from OSS
Differential Revision: D18343464
fbshipit-source-id: c1ba3a06afc40d928e59500b7b35c9e6c8720028
