Revert of DevTools: [CodeMirror] roll codemirror to version 4.1, rev@6ab1283f (https://codereview.chromium.org/247773002/)

Reason for revert:
This roll breaks search experience via Ctrl-F shortcut.

Original issue's description:
> DevTools: [CodeMirror] roll codemirror to version 4.1, rev@6ab1283f
> 
> This roll fixes couple of bugs and supports chromium overlay scrollbars.
> 
> TBR=vsevik, pfeldman
> BUG=359068
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=172161

TBR=pfeldman@chromium.org,vsevik@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=359068

Review URL: https://codereview.chromium.org/248153004

git-svn-id: svn://svn.chromium.org/blink/trunk@172347 bbb929c8-8fbe-4397-9dbb-9b2b20218538