[webcrypto] Remove support for SHA-224 (CL 1 or 3).

Blink side of the change.

This was removed by the spec: https://dvcs.w3.org/hg/webcrypto-api/rev/3f7df730b2c7

BUG=245025

Review URL: https://codereview.chromium.org/194013003

git-svn-id: svn://svn.chromium.org/blink/trunk@168959 bbb929c8-8fbe-4397-9dbb-9b2b20218538