Merge pull request #19375 from akka/revert-19250-wip-fix-multipart-model-java6-ktoso

Revert "!htc fix multipart model (java6 had trouble)"

akka-stream-tests/src/test/java/akka/stream/javadsl/TcpTest.java

@@ -95,8 +95,7 @@ public class TcpTest extends StreamTest {
           } catch (BindFailedException e) {
             // expected
           } catch (Exception e) {
-            // throw new AssertionError("failed", e); // TODO: bring back once we're JDK7+
-            throw new RuntimeException("failed", e);
+            throw new AssertionError("failed", e);
           }
           return null;
         }