Fix remove_delayed_selection to ignore last_enqueued_at redis key

When `remove_delayed_selection` encounters the `last_enqueued_at` redis key, it explodes violently with the error:

    Redis::CommandError:
        ERR Operation against a key holding the wrong kind of value

This PR fixes it by rejecting the key from the jobs set in `remove_delayed_selection`, and adds a test to ensure that it passes when the key exists.

Also took the liberty of adding myself to the AUTHORS.md, because apparently that's part of the PR guidelines ;)