Remove failure continuations.

They are no longer necessary.  Try/catch establishes a catchError
handler for the future so await doesn't need one.
Merge branch 'remove-error-cont' of https://github.com/kmillikin/async_await into remove-error-cont
Merge branch 'master' into remove-error-cont
Merge pull request #42 from kmillikin/remove-error-cont

Remove error cont