Remove RUBY_API_VERSION check in cxxanyargs.hpp

The version check used undefined macros, causing -Wundef warnings.
The conditional is no longer needed as Ruby is past version 3.1.

Author: heathdutton

include/ruby/backward/cxxanyargs.hpp

@@ -510,9 +510,7 @@ struct driver {
          * this writing the  version is 2.8.  Let's warn this  later, some time
          * during 3.x.   Hopefully codes in  old (ANYARGS-ed) format  should be
          * less than now. */
-#if (RUBY_API_VERSION_MAJOR * 100 + RUBY_API_VERSION_MINOR) >= 301
         RUBY_CXX_DEPRECATED("use of ANYARGS is deprecated")
-#endif
         /// @copydoc define(VALUE klass, T mid, U func)
         /// @deprecated  Pass correctly typed function instead.
         static inline void