insns.def: remove redundant ifndef in r63988

By the way, the original patch of r63988 was provided by wanabe:
https://github.com/wanabe/ruby/tree/local-stack

but I forgot to add his credit in the previous commit message.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63990 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

insns.def

@@ -1270,9 +1270,7 @@ opt_aset_with
     else {
 #ifndef MJIT_HEADER
         PUSH(recv);
-#ifndef MJIT_HEADER
         PUSH(rb_str_resurrect(key));
-#endif
         PUSH(val);
         ADD_PC(-WIDTH_OF_opt_send_without_block);
 #endif