Remove unnecessary cast for DfsReader

Change-Id: I22aaccfc9d589750f9d1d711b655dd0fd543fa57
Signed-off-by: Zhen Chen <czhen@google.com>

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsGarbageCollector.java

@@ -235,7 +235,7 @@ public class DfsGarbageCollector {
 					JGitText.get().supportOnlyPackIndexVersion2);
 
 		startTimeMillis = SystemReader.getInstance().getCurrentTime();
-		ctx = (DfsReader) objdb.newReader();
+		ctx = objdb.newReader();
 		try {
 			refdb.refresh();
 			objdb.clearCache();

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsPackCompactor.java

@@ -201,7 +201,7 @@ public class DfsPackCompactor {
 			pm = NullProgressMonitor.INSTANCE;
 
 		DfsObjDatabase objdb = repo.getObjectDatabase();
-		try (DfsReader ctx = (DfsReader) objdb.newReader()) {
+		try (DfsReader ctx = objdb.newReader()) {
 			PackConfig pc = new PackConfig(repo);
 			pc.setIndexVersion(2);
 			pc.setDeltaCompress(false);