These files indicate to Maven that it attempted to obtain the archive by download, but was unsuccessful. In order to save bandwidth it will not attempt this again until a certain time period encoded in the file has elapsed. The command line switch -U force maven to perform the update before the retry period. This may be necessary if you attempted to build while disconnected from the network.
The method of removing the files works with most versions of maven, but since the files are internal mementos to maven, I would not recommend this method. There is no guarantee that this information is not referenced or held elsewhere and such manipulation can damage the system.