Cleanup BUILD.bazel (#38699)
Summary:
Use recursive glob to make `aten_headers` and `torch_headers` declaration more compact
Use list generator to define torch_cpp_api tests
Pull Request resolved: https://github.com/pytorch/pytorch/pull/38699
Differential Revision: D21635357
Pulled By: malfet
fbshipit-source-id: ecab437d471b6be0c3caf669d4f59fcda9409249
