AIModelDownloadProgressManager: Don't report already downloaded components

If a component is already downloaded, it removes it from the list of
components it reports on. Meaning we won't wait to observe their total
bytes and we won't include their total bytes or downloaded bytes in the
calculation of the progress event.

Bug: 393553575, 391712889, 381969774, 391715395
Change-Id: I367ea672fb56481a5821798edb941713fd54d6df
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6306269
Reviewed-by: Mingyu Lei <leimy@chromium.org>
Commit-Queue: Nathan Memmott <memmott@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1430967}