Remove unused header inclusion (#119667)

Fixes #ISSUE_NUMBER

Pull Request resolved: https://github.com/pytorch/pytorch/pull/119667
Approved by: https://github.com/Skylion007

torch/csrc/autograd/python_engine.cpp

@@ -22,7 +22,6 @@
 #endif
 
 #include <memory> // for unique_ptr
-#include <unordered_set>
 #include <utility>
 
 using namespace torch::autograd;