[1.8] Remove torch.vmap (#52397)
torch.vmap is a prototype feature and should not be in the stable
binary. This PR:
- Removes the `torch.vmap` API
- Removes the documentation entry for torch.vmap
- Changes the vmap tests to use an internal API instead of torch.vmap.
Test Plan:
- Tested locally (test_torch, test_autograd, test_type_hints, test_vmap), but also wait
for CI.
