Summary:
Now that `exception_wrapper` can access the exception object directly from the `std::exception_ptr`, it no longer needs to be passed the exception object separately.

This eliminates duplicative `catch (exception const&)` clauses which primarily construct `exception_wrapper` instances, reducing build artifact size.

Reviewed By: akrieger

Differential Revision: D27888763

fbshipit-source-id: 5f60a07083b3c8d818f0eafd5b17afcfca239ab8