Revert 237409 "Move PreferencesMac to components/policy/."

> Move PreferencesMac to components/policy/.
> 
> This facilitates the refactoring of chrome/browser/policy into a layered
> component.
> 
> BUG=271392
> 
> Review URL: https://codereview.chromium.org/78603003

TBR=dconnelly@chromium.org

Review URL: https://codereview.chromium.org/89223003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237412 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237412