* Update external plugin documentation source
The Linode plugin for Packer is now maintained by the Linode team, under
their respective GitHub org. This changes updates the source address for
the external plugin that should be used for pulling new plugin
documentation.
* Removed packer-plugin-linode for list of vendored plugins
The Linode plugin for Packer is now maintained by the Linode team, under
their respective GitHub org. This changes removes Linode from the vendored plugins
lists.