=str Clean up Source#combine instance method code. (#31188)

akka-stream/src/main/scala/akka/stream/scaladsl/Source.scala

@@ -231,20 +231,7 @@ final class Source[+Out, +Mat](
   @deprecated("Use `Source.combine` on companion object instead", "2.5.5")
   def combine[T, U](first: Source[T, _], second: Source[T, _], rest: Source[T, _]*)(
       strategy: Int => Graph[UniformFanInShape[T, U], NotUsed]): Source[U, NotUsed] =
-    Source.fromGraph(GraphDSL.create() { implicit b =>
-      import GraphDSL.Implicits._
-      val c = b.add(strategy(rest.size + 2))
-      first ~> c.in(0)
-      second ~> c.in(1)
-
-      @tailrec def combineRest(idx: Int, i: Iterator[Source[T, _]]): SourceShape[U] =
-        if (i.hasNext) {
-          i.next() ~> c.in(idx)
-          combineRest(idx + 1, i)
-        } else SourceShape(c.out)
-
-      combineRest(2, rest.iterator)
-    })
+    Source.combine(first, second, rest: _*)(strategy)
 
   /**
    * Transform this source whose element is ``e`` into a source producing tuple ``(e, f(e))``