remove / rewrite weak module tests (#31193)
Summary:
Remove most of the testing for `weak_script`, since we removed it. Refactor a few of the existing tests to use recursive scripting api.
Fix for https://github.com/pytorch/pytorch/issues/23965
Pull Request resolved: https://github.com/pytorch/pytorch/pull/31193
Differential Revision: D18966291
Pulled By: eellison
fbshipit-source-id: 6b1e18c293f55017868a14610d87b69be42bde12
