[ONNX] Add eliminate_unused_items pass (#38812)

Summary:
This PR:

- Adds eliminate_unused_items pass that removes unused inputs and initializers.
- Fixes run_embed_params function so it doesn't export unnecessary parameters.
- Removes  test_modifying_params in test_verify since it's no longer needed.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/38812

Reviewed By: ezyang

Differential Revision: D22236416

Pulled By: houseroad

fbshipit-source-id: 30e1a6e8823a7e36b51ae1823cc90476a53cd5bb

torch/csrc/jit/python/init.cpp

@@ -31,6 +31,7 @@
 #include <torch/csrc/jit/passes/onnx.h>
 #include <torch/csrc/jit/passes/onnx/cast_all_constant_to_floating.h>
 #include <torch/csrc/jit/passes/onnx/constant_fold.h>
+#include <torch/csrc/jit/passes/onnx/eliminate_unused_items.h>
 #include <torch/csrc/jit/passes/onnx/fixup_onnx_conditionals.h>
 #include <torch/csrc/jit/passes/onnx/fixup_onnx_loop.h>
 #include <torch/csrc/jit/passes/onnx/function_substitution.h>
@@ -156,6 +157,16 @@ void initJITBindings(PyObject* module) {
             return paramsDict;
           },
           pybind11::return_value_policy::move)
+      .def(
+          "_jit_pass_onnx_eliminate_unused_items",
+          [](std::shared_ptr<Graph>& graph,
+             std::map<std::string, IValue>& paramsDict) {
+            EliminateUnusedItemsONNX(
+                graph->block(),
+                paramsDict); // overload resolution
+            return paramsDict;
+          },
+          pybind11::return_value_policy::move)
       .def("_jit_pass_onnx_scalar_type_analysis", ScalarTypeAnalysisForONNX)
       .def(
           "_jit_pass_onnx_prepare_inplace_ops_for_onnx",