Revert 254672 "Replace the custom ProxyConfigServiceDirect class..."

> Replace the custom ProxyConfigServiceDirect class with the equivalent
> net::ProxyConfigServiceFixed class.
> 
> R=eroman@chromium.org,stgao@chromium.org,rlarocque@chromium.org
> BUG=none
> TEST=none
> 
> Review URL: https://codereview.chromium.org/180283003

This is the best candidate for issue 348951

TBR=wtc@chromium.org

Review URL: https://codereview.chromium.org/178463017

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254753 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254753