remove unused Exceptions in WorkerStorage

there are many unused Exceptions in WorkerStorage, which methods doesn't throw at all.
Hi @shimingfei, thanks for trying to address my comment but what I meant to say was that each pull request (PR) should contain non side effect changes that specific to the description of the PR.
In this case, you mix between remove extra exceptions and adding final modifiers to member variables. 
This mix of pull requests will make it harder if we need to port the PR to different branch because it contains additional changes that not covered by the description and original intent of the PR.