PERF: mark posts for rebake vs forcing a rebake inline when migrating to s3

Rebaking posts can be expensive instead of blocking here simply mark posts
for rebake.

We can then work through them faster in other jobs, plus this should not
hold of a datacenter migration.

lib/tasks/uploads.rake

@@ -475,13 +475,10 @@ def migrate_to_s3
         .where("u.id IS NOT NULL AND u.url LIKE '//%' AND optimized_images.url NOT LIKE '//%'")
         .delete_all
 
-      puts "Rebaking posts with lightboxes..."
+      puts "Flagging all posts containing oneboxes for rebake..."
 
-      Post.where("cooked LIKE '%class=\"lightbox\"%'").find_each do |post|
-        putc "."
-        post.rebake!(priority: :ultra_low)
-      end
-      puts
+      count = Post.where("cooked LIKE '%class=\"lightbox\"%'").update_all(baked_version: Post::BAKED_VERSION - 1)
+      puts "#{count} posts were flagged for a rebake"
     end
   end