[errors] Greatly simplify common/errors package.

logdog/common/storage/entry.go

Index: logdog/common/storage/entry.go
diff --git a/logdog/common/storage/entry.go b/logdog/common/storage/entry.go
index 2ff78ff2c7f31681a36c05d25984000681c373b0..5df9607c22db3c753ac9849b90145647836deab2 100644
--- a/logdog/common/storage/entry.go
+++ b/logdog/common/storage/entry.go
@@ -68,7 +68,7 @@ func (e *Entry) GetLogEntry() (*logpb.LogEntry, error) {
 
 		var le logpb.LogEntry
 		if err := proto.Unmarshal(e.D, &le); err != nil {
-			return nil, errors.Annotate(err).Reason("failed to unmarshal").Err()
+			return nil, errors.Annotate(err, "failed to unmarshal").Err()
 		}
 		e.le = &le
 	}