Remove fully qualified weak script names (#15364)
Summary:
Cleanup to make references to `weak_script` consistent across codebase
Pull Request resolved: https://github.com/pytorch/pytorch/pull/15364
Differential Revision: D13509676
Pulled By: driazati
fbshipit-source-id: 93dbbbe57e9b9b6587895f3cc6fac678babd21de
