Simplify ScriptModule bindings. (#29432)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/29432
This removes a lot of the private methods on torch._C.ScriptModule,
and instead implements functionality in terms of slot_dict_impl views
to implement _parameter, _buffers, and _modules in nn.Module.
A followup PR should also remove the _register_attribute,
_register_module, and _register_parameter methods, but this requires
more refactoring of the way tracing creates modules and replication
for data parallel works.
Test Plan: Imported from OSS
Differential Revision: D18387963
Pulled By: zdevito
fbshipit-source-id: f10d47afeb30c1e05d704ae5ac4166830933125c
