Revert "fix: migrate empty tags as []"

This reverts commit 3c611393.

program/migrations/0073_alter_note_tags.py

@@ -12,11 +12,6 @@ def split_old_tags(apps, _):
 
         note.save()
 
-    for note in Note.objects.filter(old_tags=""):
-        note.tags = json.dumps([])
-
-        note.save()
-
 
 class Migration(migrations.Migration):
     dependencies = [