Remove wrong assert in LocalCheckpointTrackerTests

It's possible for the set "seqNos" to contain only the "unFinishedSeq"
in the testConcurrentReplica test. If this is the case, the call
`randomValueOtherThan` won't make any progress because the predicate
will never be false.

This commit removes this expectation because it's incorrect and it's no
longer needed as we have a dedicated test to verify the contains method.

Relates #33871

server/src/test/java/org/elasticsearch/index/seqno/LocalCheckpointTrackerTests.java

@@ -218,7 +218,6 @@ protected void doRun() throws Exception {
         }
         assertThat(tracker.getMaxSeqNo(), equalTo(maxOps - 1L));
         assertThat(tracker.getCheckpoint(), equalTo(unFinishedSeq - 1L));
-        assertThat(tracker.contains(randomValueOtherThan(unFinishedSeq, () -> (long) randomFrom(seqNos))), equalTo(true));
         assertThat(tracker.contains(unFinishedSeq), equalTo(false));
         tracker.markSeqNoAsCompleted(unFinishedSeq);
         assertThat(tracker.getCheckpoint(), equalTo(maxOps - 1L));