Remove unnecessary backward code

Author: samanklesaria

src/libtorchaudio/rnnt/autograd.cpp

@@ -1,22 +1,8 @@
 #include <libtorchaudio/rnnt/compute.h>
 
 namespace torchaudio {
-namespace rnnt {
 
 
-
-  static torch::autograd::tensor_list backward(
-      torch::autograd::AutogradContext* ctx,
-      torch::autograd::tensor_list grad_outputs) {
-    auto saved = ctx->get_saved_variables();
-    auto grad = saved[0];
-    auto grad_out = grad_outputs[0].view({-1, 1, 1, 1});
-    auto result = grad * grad_out;
-    torch::Tensor undef;
-    return {result, undef, undef, undef, undef, undef, undef, undef};
-  }
-}
-
 TORCH_LIBRARY_FRAGMENT(torchaudio, m) {
   m.def("torchaudio::rnnt_loss_forward", &rnnt_loss);
 }