views: Cleanup stubs_aura.cc.

Remove a lot of unused forward declarations and unused includes.

BUG=None
TEST=None
TBR=ben@chromium.org

Review URL: https://codereview.chromium.org/30593002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229606 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 229606