docs: Remove unnecessary `hexo-generator-*` plugins.
docs: Remove unnecessary `hexo-generator-*` plugins.

Generators are used for generating additional content in Hexo.  While these
are great for making a blog (for example, `hexo-generator-index` to put all
your blog posts on an index page, `hexo-generator-tag` to keep a page updated
with all your trending blog tags, and `hexo-generator-archive` if you want to
store your aging content somewhere where nobody will find it), they don't seem
to be at all necessary for our purposes, which are documentation.

Unfortunately, they are in the default skeleton of a new Hexo project and they
don't seem to have ever been removed from our non-blog docs deployments,
despite the fact that they seem unnecessary.

In an effort to drastically reduce the overhead of maintaining these docs
deployments, I'm removing these as "unnecessary" until proven otherwise.

apollostack/apollo-server