MINOR: Remove line for testing repartition topic name (#6488)

With KIP-307 joined.name() is deprecated plus we don't need to test for repartition topic names.
Reviewers: Matthias J. Sax <mjsax@apache.org>

streams/streams-scala/src/test/scala/org/apache/kafka/streams/scala/kstream/JoinedTest.scala

@@ -42,6 +42,5 @@ class JoinedTest extends FlatSpec with Matchers {
     joined.keySerde.getClass shouldBe Serdes.String.getClass
     joined.valueSerde.getClass shouldBe Serdes.Long.getClass
     joined.otherValueSerde.getClass shouldBe Serdes.Integer.getClass
-    joined.name() shouldBe repartitionTopicName
   }
 }