Delete duplicate test (#7412)

* Delete duplicate test

StartTask was exactly the same as CreateTask 50 lines above.

* Restore poorly merged test case

tests/FSharp.Core.UnitTests/FSharp.Core/Microsoft.FSharp.Control/AsyncType.fs

@@ -199,20 +199,6 @@ type AsyncType() =
             | _ -> reraise()
         Assert.IsTrue (tcs.Task.IsCompleted, "Task is not completed")
 
-    [<Test>]
-    member this.StartTask () =
-        let s = "Hello tasks!"
-        let a = async { return s }
-#if !NET46
-        let t = 
-#else
-        use t =
-#endif
-            Async.StartAsTask a
-        this.WaitASec t
-        Assert.IsTrue (t.IsCompleted)
-        Assert.AreEqual(s, t.Result)    
-
     [<Test>]
     member this.RunSynchronouslyCancellationWithDelayedResult () =
         let cts = new CancellationTokenSource()