Simplify ipfs rm command logic by extracting it into a separate function instead of having a giant loop.

This PR is actually needed for #8447 but it's submitted separately because it's:

• independent to be reviewed on its own
• delicate enough to be valuable to extract it from the original PR diff
• can catch any problems sooner rather than later

(simpler to review with a split diff, and also maybe with the whitespace option)