Revert "[quant][ao_migration] `torch.nn.quantizable` → `torch.ao.nn.quantizable`. (#78717)"
This reverts commit e0876feb493d4378d5aedced367eeaae75339741.
Reverted https://github.com/pytorch/pytorch/pull/78717 on behalf of https://github.com/janeyx99 due to sorry, reverting so https://github.com/pytorch/pytorch/pull/78713 could be cleanly reverted
