This resolves some naming confusion that previously existed
as a result of DownloadThread also being used for removals.
Some related variables (e.g. activeDownloadCount) would refer
to both download and removal tasks, whilst others
(e.g. maxParallelDownloads) would refer only to downloads.
This change renames those that refer to both to use "task"
terminology.
This change also includes minor test edits.
PiperOrigin-RevId: 245913671
6b34ade908