Remove hasFailedOrCanceledSubresources.

This was used to skip caching sheets across documents that had failed
resource loads so that when you loaded a new tab with the same resource
we'd attempt to load it again.

The cross document cache (which was only used by <link>) doesn't exist
in Sky, and neither does CSSStyleSheetResource which used it, so we can
remove all this code.

R=ojan@chromium.org

Review URL: https://codereview.chromium.org/799113003