xfstests 219: ignore duplicates reported by repquota

xfstests 219: ignore duplicates reported by repquota

Arrange to ignore duplicate entries reported by the repquota command.
This can happen if an id is used more than once (such as when two user
names are assigned the same uid).

Do this here by simply dropping any reported entries whose id number
has already been seen in the output.

Signed-off-by: Alex Elder <aelder@sgi.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>