Remove workaround for GCC < 3 ios_base absence.

Source/cmStandardIncludes.h

@@ -146,11 +146,6 @@ extern int putenv (char *__string) __THROW;
 #define for if(false) {} else for
 #endif
 
-// Provide std::ios_base on ancient GCC 2.9x
-#if defined(__GNUC__) && __GNUC__ < 3
-namespace std { typedef ios ios_base; }
-#endif
-
 // check for the 720 compiler on the SGI
 // which has some strange properties that I don't think are worth
 // checking for in a general way in configure