remove duplicated headers - update cmake accordingly git-svn-id: https://sfml.svn.sourceforge.net/svnroot/sfml/branches/sfml2@1716 4e206d99-4929-0410-ac5d-dfc041789085
git-svn-id: https://sfml.svn.sourceforge.net/svnroot/sfml/branches/sfml2@1550 4e206d99-4929-0410-ac5d-dfc041789085