Remove TinyXML-1

This removes the TinyXML source files, removes it from CMakeLists.txt,
removes all the includes, and removes the functions
FILESYSTEM_saveTiXmlDocument() and FILESYSTEM_loadTiXmlDocument() (use
FILESYSTEM_saveTiXml2Document() and FILESYSTEM_loadTiXml2Document()
instead).

Additionally I've cleaned up the tinyxml2.h include in FileSystemUtils.h
so that it doesn't actually include tinyxml2.h unnecessarily, meaning a
change to TinyXML2 shouldn't rebuild all files that include
FileSystemUtils.h.

desktop_version/src/Input.cpp

@@ -3,7 +3,6 @@
 
 #include "MakeAndPlay.h"
 
-#include "tinyxml.h"
 #include "tinyxml2.h"
 
 #include "FileSystemUtils.h"