You can remove captions while using One-Click Postage and that small box that appears when you hover on one of the quick-reblog icons.

To do so:

1. Hover over the icon (Reblog, Queue, Draft)
2. Click on the Caption bar
3. Press space bar once
4. Click on the “________ Now” button.
5. The post will be reblogged/drafted/queued without any captions.