Prior to this change, concurrency was limited within a BaseDownloadController instance. However, when the RemoteResourceController (extending BaseDownloadControlller) is processing RemoteResources, a separate limit was used for each. E.g. if there were 100 RemoteResources being processed, 100 limits would be processed in parallel, leading to excessive load.
After this change, the limit is global -- 100 RRs with 1 kube resource each and 1 RR with 100 kube resource will have the same load on the api server: 10 kube resources processed in parallel.
Limit concurrency.