Revert "Legalize BFloat16 in NNC. (#83988)"
This reverts commit b049493ed52292c344c5b17f6db16a0242419865.
Reverted https://github.com/pytorch/pytorch/pull/83988 on behalf of https://github.com/clee2000 due to broke slow tests in trunk, https://github.com/pytorch/pytorch/actions/runs/3084421000/jobs/4986706931
