Revert of DevTools: Fix obsolete section.rule in StylesSidebarPane (https://codereview.chromium.org/152643004/)

Reason for revert:
Broke a bunch of inspector/styles tests.

Original issue's description:
> DevTools: Fix obsolete section.rule in StylesSidebarPane
> 
> This patch fixes a bug in StyleSideBar sections that didn't update section().rule property.
> 
> R=apavlov@chromium.org
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=166312

TBR=apavlov@chromium.org,lushnikov@chromium.org
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/134133007

git-svn-id: svn://svn.chromium.org/blink/trunk@166315 bbb929c8-8fbe-4397-9dbb-9b2b20218538