Delete tasks related to site_keys.rb
Delete tasks related to site_keys.rb

- Delete tasks related to site_keys.rb as
  it is no longer being used.

- Refer to Scott's comment on Github
  https://github.com/concord-consortium/rigse/pull/26#issuecomment-15240475

concord-consortium/rigse,concord-consortium/rigse,concord-consortium/rigse,concord-consortium/rigse,concord-consortium/rigse,concord-consortium/rigse