Remove smp_wmb() in do_migrate_proc

Migrate daemon is single thread. We don't need it.
remove migrate_done but it doesn't work
Fixed. There are sequential dependency in id of a segment

- Only increment seg->id after finished waiting
- seg->id must be initialized to zero
Remove flush_done
Merge branch 'feature/change-completion-to-id' into develop

delete flush_done and migrate_done