Remove deprecated torch.lstsq (#70980)
The time has come to remove deprecated linear algebra related functions. This PR removes `torch.lstsq`.
There's a note in `tools/codegen/gen.py` about `lstsq` schema in `native_function.yaml` that I will not remove:
https://github.com/pytorch/pytorch/blob/87139d8532c99ff5dbeef1b97948d71793aa7851/tools/codegen/gen.py#L734-L770
cc @jianyuh @nikitaved @pearu @mruberry @walterddr @IvanYashchuk @xwang233 @Lezcano
Pull Request resolved: https://github.com/pytorch/pytorch/pull/70980
Approved by: https://github.com/lezcano, https://github.com/kit1980
