Revert of Push API: define push event on Service Worker. (https://codereview.chromium.org/285403002/)

Reason for revert:
Broke all builds: http://build.chromium.org/p/chromium.webkit/console

e.g.
http://build.chromium.org/p/chromium.webkit/builders/Linux%20ChromiumOS%20Builder/builds/51757/steps/compile/logs/stdio

TBR=jochen@chromium.org
NOTREECHECKS=true
NOTRY=true

Original issue's description:
> Push API: define push event on Service Worker.
> 
> BUG=350394
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=175652

Review URL: https://codereview.chromium.org/319973002

git-svn-id: svn://svn.chromium.org/blink/trunk@175653 bbb929c8-8fbe-4397-9dbb-9b2b20218538