Update for DeprecationsURLBase

Cleaned up variable names from last night's change (confused people that I didn't expect to see it yet - git n00b)... allows us to add a DeprecationsURLBase key to preferences.plist that works effectively like LocalCatalogURLBase but only caches deprecated updates.  The net effect is that catalogs will direct swupd to Apple to download current updates, but direct to the local cache for deprecated updates.