Remove grace period from vault config section

[eikenb]

Now with our updated dependencies Vault no longer uses the grace period, it is officially deprecated as of Vault 0.5.0 (2016). It should be removed from the config documentation and either noted as being deprecated in use in the code or removed entirely.

I'll check with the Vault people about whether we should keep passing it or not. It really depends on if there are still Vault installations out there of versions < 0.5.0. If you happen to use Vault < 0.5.0, please add a comment.

[eikenb]

I spoke with the Vault team and they said that their users tend to stay pretty recent and they haven't seen any sort of support questions about versions of vault that old in a long time.

I.E. they said maintaining compatibility with that old a release is not necessary and should not be a priority.

[eikenb]

This ticket is just about getting the docs updated as I want to get that done. See #1268 for issue about removing the dead grace code.