[trivial] No way to override `AuthorizedKeysFile`

No way to override AuthorizedKeysFile for legacy default behavior.

A) I cannot override this with
   `default['openssh']['server']['authorized_keys_file'] = nil`.  Value
    shipped with cookbook gets merged.

B) It might be the default behavior on newer distributions, but not for
   older enterprise-y distros.

C) The default value of `.ssh/authorized_keys .ssh/authorized_keys2` as
   documented in the manpage cannot be set manually by attribute
   override.  Ironically, the daemon cannot parse past the first value.
   The default behavior is hardcoded into OpenSSH at a lower-level.

D) Pissed off users, every time it regresses to .ssh/authorized_keys
   only.