Remove `insert_prepack_unpack` and `fold_prepack` for now (#30909)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/30909
`fold_prepack` doesn't work anymore after we change `scale`, `zero_point`
to be attributes, but since the freeze API is coming up, I don't want to
spend time to make this work since this will be thrown away later.
Test Plan:
.
Imported from OSS
Differential Revision: D18864537
fbshipit-source-id: 649e6b91f2b04b8babacc0afb6bc1530ed7259d3
