Remove const char string comparison helper.

It is now unused.

Source/cmStandardIncludes.h

@@ -462,12 +462,6 @@ struct cmStrCmp {
     return strcmp(input, m_test.c_str()) == 0;
   }
 
-  // For use with binary_search
-  bool operator()(const char *str1, const char *str2) const
-  {
-    return strcmp(str1, str2) < 0;
-  }
-
 private:
   const std::string m_test;
 };