Remove addSubresourceAttributeURLs and addSubresourceStyleURLs

This patch removes addSubresourceAttributeURLs and
addSubresourceStyleURLs. These were previously used for
webarchive support which has since departed. No new tests as
this is just a refactoring.

Review URL: https://codereview.chromium.org/109143007

git-svn-id: svn://svn.chromium.org/blink/trunk@164283 bbb929c8-8fbe-4397-9dbb-9b2b20218538