vm_core.h: redefined_flag in rb_vm_t

* vm_core.h (struct rb_vm_struct): move redefined_flag from
  ruby_vm_redefined_flag.

* vm_core.h (BASIC_OP_UNREDEFINED_P): move from vm_insnhelper.h.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46858 b2dd03c8-39d4-4d8f-98ff-823fe69b080e