Change description:
Remove SharedWorker.workerStart because it has been deprecated and is not used. In the future, developers should use performance.timeOrigin.

Changes to API surface:
* SharedWorker.workerStart

Links:
Removal discussion: https://bugs.chromium.org/p/chromium/issues/detail?id=695996

Support in other browsers:
Internet Explorer: No
Firefox: No (but they already have performance.timeOrigin)
Safari: No