pull: Fold together deltapart+fallback count for display

pull: Fold together deltapart+fallback count for display

It's just simpler, and I'm not sure people are going to care
much about the difference by default.

We already folded in the fallback sizes into the download totals, so folding in
the count makes things consistent; previously you could see e.g.
`3/3 parts, 100MB/150MB` and be confused.

Closes: #678
Approved by: giuseppe