Revert of Expose events in workers as per latest DOM specification (https://codereview.chromium.org/262173006/)

Reason for revert:
This may be causing issues with thread safety. I am reverting until I get a chance to investigate.

Original issue's description:
> Expose events in workers as per latest DOM specification
> 
> Expose events in workers as per latest DOM specification:
> https://github.com/whatwg/dom/commit/0f69e7175dcae9edffa636bb213991330d225bf3
> 
> This CL exposes Event, CustomEvent and EventTarget to Workers and not only
> in the primary global scope (Window), as per the latest DOM specification.
> 
> Firefox 29 exposes both Event and EventTarget to workers but not CustomEvent
> (known bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1003432).
> IE11 exposes Event only to workers.
> 
> R=arv@chromium.org, tkent@chromium.org
> BUG=370011
> TEST=webexposed/global-constructors-listing-dedicated-worker.html
> TEST=webexposed/global-constructors-listing-shared-worker.html
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=173328

TBR=arv@chromium.org,tkent@chromium.org,eseidel@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=370011

Review URL: https://codereview.chromium.org/267363003

git-svn-id: svn://svn.chromium.org/blink/trunk@173525 bbb929c8-8fbe-4397-9dbb-9b2b20218538