Revert "`kl_div`: fix for grads wrt `target`, double backward, forward-over-reverse AD support. (#79007)"
This reverts commit 72ad222cff59cbe730a49dd828cb0a25d2a18417.
Reverted https://github.com/pytorch/pytorch/pull/79007 on behalf of https://github.com/janeyx99 due to Broke test_fn_fwgrad_bwgrad_nn_functional_kl_div_cpu_float64 on trunk https://hud.pytorch.org/minihud?name_filter=pull%20/%20linux-xenial-py3.7-clang7-asan%20/%20test%20(default,%202,%205,%20linux.2xlarge)
