The methods in AsyncTableRegionLocator should not throw IOException directly

Remove the throws part for the following 3 methods in AsyncTableRegionLocator: getStartKeys getEndKeys getStartEndKeys It is a mistake and we will never throw exception directly from these methods. The should get the exception from the returned CompletableFuture. In order to not introduce new methods and make more confusing, we just remove the throws part. It is an incompatible change, you may need to change your code to remove the catch section when you upgrade to HBase 3.x.