[FastTextAutosizer] Remove isFingerprintingCandidate and nextChildSkippingChildrenOfBlocks

This trivial patch removes two declarations that have no implementaiton.

BUG=

Review URL: https://codereview.chromium.org/259763006

git-svn-id: svn://svn.chromium.org/blink/trunk@172792 bbb929c8-8fbe-4397-9dbb-9b2b20218538