Use Kolibri's FileDownloader

[starnight]

We tried to fix download speed issue with Vendor old file download code.

However, Kolibri made some big change for FileDownloader since the commit ("Simplify Transfer subclasses now that they don't need to expose iterators.") included by v0.16.0-alpha19(+). And, our fix conflicts to the change and leads issue Download content failed after update Kolibri to v0.16.0-beta0.

I think this is the time using Kolibri's FileDownloader again.

Fixes: #728

[dbnicholson]

It would be nice to verify that downloads are actually fixed, but I think this is for the best and any further regressions should probably be pursued upstream.

[starnight]

Tested download speed of Artist package with Endless Key (Windows) 6.31.2.0 in Taipei office

• Start: 2023-08-07 13:41:22
• End: 2023-08-07 13:46:32

=> 5 minutes and 10 seconds -> Looks like around the speed as before.

[vanessa-chang]

Test on a chromebook, the download time takes longer compared to the production page.