remove assertion for hidden objects.

* vm_insnhelper.h (PUSH): r63763 increase "PUSH()" op and it reveals that
  there are hidden objects (at least T_IMEMO/iseq objects) are located
  on VM stack. Remove this check and I'll revisit it later.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63765 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

vm_insnhelper.h

@@ -47,7 +47,7 @@ rb_obj_hidden_p(VALUE obj)
     }
 }
 
-#define PUSH(x) (VM_ASSERT(!rb_obj_hidden_p(x)), SET_SV(x), INC_SP(1))
+#define PUSH(x) (SET_SV(x), INC_SP(1))
 #define TOPN(n) (*(GET_SP()-(n)-1))
 #define POPN(n) (DEC_SP(n))
 #define POP()   (DEC_SP(1))