Remove operator< for WebURL

This API has no more clients. The API won't be suppored once we switch WebURL
to using WebString instead of WebCString.

R=ojan
BUG=261412

Review URL: https://chromiumcodereview.appspot.com/20374004

git-svn-id: svn://svn.chromium.org/blink/trunk@154943 bbb929c8-8fbe-4397-9dbb-9b2b20218538