[PyTorch] Remove extra RNN.cpp file (#53169)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/53169
As title, there are two `aten/src/ATen/native/RNN.cpp` in `aten_native_source_list`
ghstack-source-id: 122936706
Test Plan: CI
Reviewed By: dhruvbird, iseeyuan
Differential Revision: D26715640
fbshipit-source-id: 54717ded9b293e022a47ab7891dfd04afae48ce5
