Remove overload at::frobenius_norm(const Tensor&) (#81762)
This function is an auxiliary function for `torch.norm`. This particular
overload was not even used or tested. I hope it's not used internally
either. If it is, we can simply drop this PR
Pull Request resolved: https://github.com/pytorch/pytorch/pull/81762
Approved by: https://github.com/ngimel
