Remove unused BlobData friends.

WebCore::BlobData declares a couple of friend classes that do not seem
to exist anymore.

BUG=

Review URL: https://codereview.chromium.org/369373003

git-svn-id: svn://svn.chromium.org/blink/trunk@177565 bbb929c8-8fbe-4397-9dbb-9b2b20218538