[webkitpy] Remove leftover changelog editor methods from User.

Cleaning up the User object from unused changelog editor codepart.

BUG=none

Review URL: https://codereview.chromium.org/633503003

git-svn-id: svn://svn.chromium.org/blink/trunk@183399 bbb929c8-8fbe-4397-9dbb-9b2b20218538