DevTools: remove old Timeline front-end implementation

Now that Timeline uses tracing as its back-end it is time to remove old front-end implementation.

BUG=428700,344238,298188,359961,371276

Review URL: https://codereview.chromium.org/709423002

git-svn-id: svn://svn.chromium.org/blink/trunk@185035 bbb929c8-8fbe-4397-9dbb-9b2b20218538