Remove use of include <cmsys/IOStream.hxx> from KWSys

We no longer need this compatibility layer for the compilers we support.

Source/cmStandardIncludes.h

@@ -33,14 +33,6 @@
 // Provide fixed-size integer types.
 #include <cmIML/INT.h>
 
-// Include stream compatibility layer from KWSys.
-// This is needed to work with large file support
-// on some platforms whose stream operators do not
-// support the large integer types.
-#if defined(CMAKE_BUILD_WITH_CMAKE)
-# include <cmsys/IOStream.hxx>
-#endif
-
 #include <fstream>
 #include <iostream>
 #include <iomanip>