Unfortunately I don't have the original file anymore. I believe this file tells the disparity node which two images to use (and respective camera_info topics). You can see the expected inputs in two places:

1: in the rqt graph at the end of the article

2: under the "subscribed topics" for the "stereo_image_proc/disparity" section of the docs:https://wiki.ros.org/stereo_image_proc#stereo_image_proc.2Fdiamondback.stereo_image_proc.2Fdisparity

I think the file was mapping "image_raw" (default output of my camera) to "image_rect" (input of disparity node).

As another commenter pointed out, "rect" here means "rectified." I was not aware of image rectification at the time . There is a command in that comment to turn image raw into image rect.

I believe the way to remap the parameter without the file is to use the following example: https://docs.ros.org/en/foxy/How-To-Guides/Node-arguments.html#example