IDL: Remove support for [LogPreviousValue] extended attribute

Also remove the logSetter() overload taking an old value parameter from
the WebDOMActivityLogger interface, since there are no calls to it.

BUG=388287

Review URL: https://codereview.chromium.org/497773004

git-svn-id: svn://svn.chromium.org/blink/trunk@181643 bbb929c8-8fbe-4397-9dbb-9b2b20218538