Change C++ API test files to only include torch/torch.h (#27067)
Summary:
One of the purposes of the C++ API tests in `test/cpp/api/` should be to check that including `torch/torch.h` is a sufficient prerequisite for using all C++ frontend features. This PR change ensures that.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/27067
Differential Revision: D17856815
Pulled By: yf225
fbshipit-source-id: 49c057bd807b003e4a00f6ba73131d763a0f277a
