Revert of Perform a microtask checkpoint for document.write('<script><\/script>') (https://codereview.chromium.org/130983011/)

Reason for revert:
Broke MutationObserver consistency.


Original issue's description:
> Perform a microtask checkpoint for document.write('<script><\/script>')
> 
> http://whatwg.org/html#scriptEndTag
> 
> The spec does 'Perform a microtask checkpoint' unconditionally for 'An
> end tag whose tag name is "script"', which means that document.write
> can trigger it while a script is running.
> 
> A spec bug was filed for the similar situation with 'Provide a stable
> state' on the assumption that this was a mistake, but it was not:
> https://www.w3.org/Bugs/Public/show_bug.cgi?id=24361
> 
> Unless performing a microtask checkpoint here will lead to other
> complications, it's simpler to just align with the spec.
> 
> BUG=340322
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=166445

TBR=eseidel@chromium.org,esprehn@chromium.org,adamk@chromium.org,rafaelw@chromium.org,philipj@opera.com
NOTREECHECKS=true
NOTRY=true
BUG=340322

Review URL: https://codereview.chromium.org/153913010

git-svn-id: svn://svn.chromium.org/blink/trunk@166960 bbb929c8-8fbe-4397-9dbb-9b2b20218538