insns.def: remove unnecessary sp motion

This seems obsoleted after r62087.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62387 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

insns.def

@@ -539,9 +539,7 @@ dupn
     void *dst = GET_SP();
     void *src = STACK_ADDR_FROM_TOP(n);
 
-    INC_SP(n); /* alloca */
     MEMCPY(dst, src, VALUE, n);
-    DEC_SP(n);
 }
 
 /* swap top 2 vals */