examples with distinct URLs deleted from source-design-merge aren't deleted from gh-pages

[michaelbabyn]

Old examples that have been deleted from source-design-merge will still appear on gh-pages after running rake deploy.

We copy the newly generated jekyll site to the root directory of gh-pages branch during rake deploy (https://github.com/plotly/documentation/blob/gh-pages/Rakefile#L24) but we don't delete the old site first. This means that any page that exists on the old site but not on the new site will remain up.

This is the case for https://github.com/plotly/documentation/issues/1174.

[cldougl]

in general, we'll want to redirect many of these rather than removing (as with https://github.com/plotly/documentation/issues/1174).