alternator test: enable a passing test
alternator test: enable a passing test

After issue #7107 was fixed (regarding the correctness of OldImage and NewImage
in Alternator Streams) we forgot to remove the "xfail" tag from one of the tests
for this issue.

This test now passes, as expected, so in this patch we remove the xfail tag.

Refs #7107

Signed-off-by: Nadav Har'El <625169824b719df98706d88646d0aae6f368ae4d@scylladb.com>
Message-Id: <20200827103054.186555-1-625169824b719df98706d88646d0aae6f368ae4d@scylladb.com>

avikivity/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla