Some work on eager op binding codegen (gen_python_functions.py) (#29986)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/29986

Previously in addition to generating a python binding for each op,
we would generate an almost-trivial helper for each overload.
This PR eliminates the helpers, simplifying codegen logic a bit and
reducing the source-level indirection by a step.
Perf should be unchanged.

codegen diff: 1f2f07fb60

Note: in the interests of keeping the diff contained, there's only
some light cleanup here beyond what's necessary for the codegen changes.
Plan is to do some more substantial refactoring in followup PRs that
leave generated code unchanged.

Test Plan: Imported from OSS

Differential Revision: D18567980

Pulled By: bhosmer

fbshipit-source-id: eb9a81babb4489abd470842757af45580d4c9906

tools/autograd/templates/python_variable_methods.cpp

@@ -31,8 +31,6 @@
 #include <ATen/ATen.h>
 #include "c10/util/Optional.h"
 
-#include "python_variable_methods_dispatch.h"
-
 #include <stdexcept>
 
 using at::DeviceGuard;