Remove TODOs we're not going to do

1. customCacheKey for DASH/HLS/SS is now asserted against
   in DownloadRequest
2. Merging of event delivery in DownloadManager is very
   tricky to get right and probably not a good idea

PiperOrigin-RevId: 244048392

library/core/src/main/java/com/google/android/exoplayer2/offline/DefaultDownloaderFactory.java

@@ -98,7 +98,6 @@ public class DefaultDownloaderFactory implements DownloaderFactory {
       throw new IllegalStateException("Module missing for: " + request.type);
     }
     try {
-      // TODO: Support customCacheKey in DASH/HLS/SS, for completeness.
       return constructor.newInstance(request.uri, request.streamKeys, downloaderConstructorHelper);
     } catch (Exception e) {
       throw new RuntimeException("Failed to instantiate downloader for: " + request.type, e);

library/core/src/main/java/com/google/android/exoplayer2/offline/DownloadManager.java

@@ -485,8 +485,6 @@ public final class DownloadManager {
     return true;
   }
 
-  // TODO: Merge these three events into a single MSG_STATE_CHANGE that can carry all updates. This
-  // allows updating idle at the same point as the downloads that can be queried changes.
   private void onInitialized(List<Download> downloads) {
     initialized = true;
     this.downloads.addAll(downloads);