Revert of sync: turn on session sync v2 (https://codereview.chromium.org/130403003/)

Reason for revert:
BUG=334980

Original issue's description:
> sync: turn on session sync v2
> 
> BUG=98892
> TBR=jyasskin@chromium.org, msw@chromium.org
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=244909

TBR=zea@chromium.org,jyasskin@chromium.org,msw@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=98892

Review URL: https://codereview.chromium.org/131743028

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245682 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 245682