Get rid of WTF::SHA1.

WTF::SHA1 is redundant now with WebCrypto support in place, and Blink probably
should not roll its own crypto. This removes WTF::SHA1 and replaces its
consumers with WebCrypto calls.

BUG=349514

Review URL: https://codereview.chromium.org/189373010

git-svn-id: svn://svn.chromium.org/blink/trunk@170897 bbb929c8-8fbe-4397-9dbb-9b2b20218538