Removed checks/workarounds for pre-C++89 compatibility (#449)

After 30+ years, just assume that the following exist:
- extension-less includes
- namespaces
- std::
- static_cast
- bool

c++/examples/readdata.cpp

@@ -17,11 +17,7 @@
 //      information about the dataset in the SDS.h5 file is obtained.
 //
 
-#ifdef OLD_HEADER_FILENAME
-#include <iostream.h>
-#else
 #include <iostream>
-#endif
 using std::cout;
 using std::endl;