Remove wrong export CheckFullscreen


git-svn-id: svn+ssh://svn.code.sf.net/p/mingw-w64/code/trunk@6563 4407c894-4637-0410-b4f5-ada5f102cad1
Remove illegal export CheckFullscreen


git-svn-id: svn+ssh://svn.code.sf.net/p/mingw-w64/code/trunk@6564 4407c894-4637-0410-b4f5-ada5f102cad1